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The Skeptics' Guide to the Universe => Podcast Episodes => Topic started by: Steven Novella on September 15, 2018, 10:33:57 AM

Title: Episode #688
Post by: Steven Novella on September 15, 2018, 10:33:57 AM
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Title: Re: Episode #688
Post by: DevoutCatalyst on September 15, 2018, 02:54:58 PM
Better looking pee or your money back,
(https://cdn3.volusion.com/kceqm.mleru/v/vspfiles/photos/1751-2.jpg?1521734349)
Title: Re: Episode #688
Post by: PSXer on September 15, 2018, 03:51:27 PM
Nitpick: You mentioned that if the only criteria for being a planet was that it was round, 7 moons would be considered planets. Actually, according to Wikipedia, the count would be all the way up to 19. Maybe Dysnomia would be included too? We'll probably never know for sure. https://en.wikipedia.org/wiki/List_of_gravitationally_rounded_objects_of_the_Solar_System#Satellites

If they were all listed as planets, that would be a lot of planets. But if they're moons, they won't come up in the list of planets and will be mostly ignored. I guess kids will never learn how cool Titan is because it happens to be orbiting Saturn.  :'(

As to Haumea, I believe the current understanding for it not being round is not that it doesn't have enough mass to be squished into a ball. It's elongated because it rotates so damn fast- 1 rotation every 4 hours. Earth isn't perfectly spherical either. Is there a certain "roundness quotient" that Earth is on one side of and Haumea is on the other? I guess the does it look round by eye method you mentioned in the podcast.

Any way you stack it, you're either going to have a LOT of planets or you're going to be missing some interesting objects. Probably the only thing that really matters about something being classified as a 'planet' or not is if they teach about it in schools. I'm reminded of some guy on Slashdot who said they should reclassify rivers so that only the 8 largest are real rivers and the rest are 'dwarf rivers'. That way the kids wouldn't have too many rivers to memorize.
Title: Re: Episode #688
Post by: lonely moa on September 15, 2018, 04:56:04 PM
Not the first time I have heard a doctor make a totally wrong diagnosis, but I thought everyone knew that beetroot turns one's urine "pink".  I await the next podcast after Steve eats asparagus.
Title: Episode #688
Post by: CarbShark on September 15, 2018, 05:06:24 PM
Nitpick: You mentioned that if the only criteria for being a planet was that it was round, 7 moons would be considered planets.


If you were referring to my comment, it included directly orbiting the sun, which excludes satellites.

So no moons. A total of 9 known planets and possibly one more

(If you were not referring to my comment, the paper arguing  Pluto be classified a planet specifically eliminated satellites. I haven’t listened to this episode yet and probably shouldn’t be commenting yet, but we discussed this at length in another thread)
Sent from my iPhone using Tapatalk
Title: Re: Episode #688
Post by: PSXer on September 15, 2018, 06:20:10 PM
Sorry should have been more clear, I was talking to the podcast. Steve said that Philip Metzger wants to change the definition of a planet to anything that's gravitationally rounded. He then said that under Metzger's definition, 7 moons would classify as planets. One of those two statements must be wrong. I guess I could see what Metzger actually said about it. I'm guessing the 7 number came about because 7 of the moons are larger than Pluto.
Title: Re: Episode #688
Post by: The Latinist on September 15, 2018, 07:15:32 PM
I’ve long advocated the same definition for planet that’s Steve does in this episode. To me, it strikes the perfect balance between tradition and science.

My impression is that planetary scientists are the main people who advocate a position that would make moons of Jupiter and Saturn planets.  From their perspective, the only things that matter are the characteristics of bodies that they study...and I think that they also believe that promoting such bodies to planetary status will give them greater priority in research funding.

Finally, since there seems to be some confusion about what exactly would count as gravitationally rounded, I’ll drop this wiki page here: https://en.m.wikipedia.org/wiki/List_of_gravitationally_rounded_objects_of_the_Solar_System.  Note that this page includes some objects which are believed formerly to have been in hydrostatic equilibrium even if they are not currently so (due, for instance, to impacts or other loss of material). Which ones will make the cut depends on where one draws the line.
Title: Re: Episode #688
Post by: elert on September 15, 2018, 07:45:38 PM
I'm sorry, but the 100 days ground zero fire bit from Science or Fiction is a bit too press-release-perfect for me. Ground zero had its own local weather for awhile. I was seeing and smelling this on my way to work every day after until some random day in November. Here's where the trouble begins. In my memory, the fire was declared out around THAT time — roughly 60 days later. I remember hearing it on either the radio or TV or both. I also remember the smell stopping around that time. I have no recollection of anyone discussing this in December 2001. More importantly, how does a fire know that a prominent base 10 number of days has passed?
Title: Re: Episode #688
Post by: mabell_yah on September 15, 2018, 10:16:17 PM
I think "Steve's law" is an improvement, and I'm happy to learn the word "barycenter." However, I don't think the concept of binary planet (and above) is meaningful. The term "planet" should refer to the important bodies of a solar system with minor refinements.

Pluto's diameter is 2372km with the barycenter 960km above the surface. Charon's diameter is 1208km with a semi-major axis (which I take to mean closest orbit) of 17,536km.  So the barycenter is 95% of Charon's orbital distance away from Charon. Furthermore, the barycenter is within a planetary diameter of Pluto, whereas it's around 14 Charon diameters away from Charon. This is s severely lopsided relationship. Calling the Pluto system a double planet and putting Charon in the same classification as Jupiter waters down the definition of planet to the point it is almost meaningless. Therefor, I suggest we refine Steve's definition to say that a planet must have it's barycenter within the planet body. Keeping it within a planetary diameter of the surface is also acceptable.

I would add a fourth rule: a planet cannot be tidally locked. Pluto and Charon are tidally locked, so out they go.

Finally, I would add a fifth rule: a planetary orbit must enter the heliosphere. Remember when Voyager passed though the heliopause and was said to have left the solar system. If it's outside the solar system, it's not a planet. It's something else. The recently-proposed planet 9 is so far out that it never enters the heliosphere. It's something else. Maybe an epi-planet.
Title: Re: Episode #688
Post by: sylvano on September 16, 2018, 02:34:45 AM
Greetings all.

Is there a URL to the WTN bird call website mentioned in the episode? I didn't notice one in the show notes.

thanks
Sylvano
Title: Re: Episode #688
Post by: lucek on September 16, 2018, 07:09:44 AM
Loved the description of starwisps.
Title: Re: Episode #688
Post by: CookieMustard on September 16, 2018, 10:15:14 AM
As a borscht lover the first thing that occured to me when Steve talked about his pinkish urine was beets. I used to make large pots of borscht which would last several days and my urine would be pinkish for the duration. Plus my wife likes making pickled beets.
I once talked about this to a friend and he mentioned that at one time he had been eating a large amount of carrots for several days and his urine had an orange tint for a while.
Title: Re: Episode #688
Post by: DevoutCatalyst on September 16, 2018, 10:51:56 AM
As a borscht lover the first thing that occured to me when Steve talked about his pinkish urine was beets. I used to make large pots of borscht which would last several days and my urine would be pinkish for the duration. Plus my wife likes making pickled beets.
I once talked about this to a friend and he mentioned that at one time he had been eating a large amount of carrots for several days and his urine had an orange tint for a while.
Sweet potatoes being my staple, I switched to light yellow fleshed varieties. The orange flesh cultivars make the skin look positively covfefe eaten daily. That was a decade ago. Nobody knows my sweet potato habit today excepting you and the greengrocer.
Title: Re: Episode #688
Post by: PabloHoney on September 16, 2018, 12:03:59 PM
My employer uses a personality test called https://www.rembrandtadvantage.com/index.html|Rembrandt (https://www.rembrandtadvantage.com/index.html|Rembrandt). 
It's always bugged the shit out of me because it's self-reported and there are sites that talk about how to respond to the questions to achieve X profile that would be better for your career and increase the likelihood of getting hired/promoted etc.. 

From what I understand though, the Rembrandt test it at least based on the accepted psychological categories and it provides values within the spectrum rather than the false dichotomies.  I've bitched about it to my boss, but find myself dialing it back a bit since it's at least quite a bit better than Myers Briggs. 

Title: Re: Episode #688
Post by: Alex Simmons on September 16, 2018, 05:25:32 PM
I would add a fourth rule: a planet cannot be tidally locked. Pluto and Charon are tidally locked, so out they go.
I'm not sure why tidal locking should be a factor as tidal locking is an inevitability of enough time passing.

With enough time (about 50 billion years) the Earth will become tidally locked to the Moon but the Sun may have vapourised the Earth or caused other gravitational interactions before that happens. Depends on how big the Sun gets in its dying stages.

Many exoplanets are tidally locked to their host star.

Mercury is tidally locked in a 3:2 spin orbit resonance.
Title: Re: Episode #688
Post by: brilligtove on September 16, 2018, 05:35:16 PM
I would add a fourth rule: a planet cannot be tidally locked. Pluto and Charon are tidally locked, so out they go.
I'm not sure why tidal locking should be a factor as tidal locking is an inevitability of enough time passing.

With enough time (about 50 billion years) the Earth will become tidally locked to the Moon but the Sun may have vapourised the Earth or caused other gravitational interactions before that happens. Depends on how big the Sun gets in its dying stages.

Many exoplanets are tidally locked to their host star.

Mercury is tidally locked in a 3:2 spin orbit resonance.

It seems like this rule is supposed to exclude Charon and include Pluto. As such it seems too specific and nit picky too me. I can see a total of four kinds of planet classes, I think. Dwarf, small rocky, large rocky, and gas giant. In each class the location would be closer than goldilocks, in goldilocks, beyond goldilocks, or beyond heliopause.
Title: Re: Episode #688
Post by: CookieMustard on September 16, 2018, 09:12:42 PM
Greetings all.

Is there a URL to the WTN bird call website mentioned in the episode? I didn't notice one in the show notes.

https://experiments.withgoogle.com/bird-sounds

It won't work on tablets, needs a desktop.
Title: Re: Episode #688
Post by: arthwollipot on September 16, 2018, 10:00:03 PM
For the record, Bob is a philistine and Australian hamburgers don't have beets on them. They have beetroot which is lightly pickled and canned. It's not like we're pulling up the roots and slicing them to put directly on our burgers. I mean, some people might, but that's neither here nor there. IT'S BEETOOT AND IT'S DELICIOUS ON HAMBURGERS SO THERE.
Title: Re: Episode #688
Post by: mabell_yah on September 17, 2018, 01:10:13 AM
Quote
I would add a fourth rule: a planet cannot be tidally locked. Pluto and Charon are tidally locked, so out they go.

My intent was do disqualify a body that can't dominate its own moons enough to keep rotating independently. I wasn't aware of tidally-locked exo-planets, but it doesn't matter. I'm sticking to my guns.

JK I learned something. Besides, the rule probably was too fiddly. Scratch rule 4.

Fun fact: The barycenter of the sun Jupiter system is about 30,000 miles outside the sun. Maybe the sun isn't a star :roflolmao:
Title: Re: Episode #688
Post by: brilligtove on September 17, 2018, 06:21:19 AM
Quote
I would add a fourth rule: a planet cannot be tidally locked. Pluto and Charon are tidally locked, so out they go.

My intent was do disqualify a body that can't dominate its own moons enough to keep rotating independently. I wasn't aware of tidally-locked exo-planets, but it doesn't matter. I'm sticking to my guns.

JK I learned something. Besides, the rule probably was too fiddly. Scratch rule 4.

Fun fact: The barycenter of the sun Jupiter system is about 30,000 miles outside the sun. Maybe the sun isn't a star :roflolmao:

Oh, I see what you were going for now. If the bodies are both tidally locked. That is less fiddly than I thought - but still too fiddly.

https://youtu.be/RzP_kIXsuvA
Title: Re: Episode #688
Post by: gebobs on September 17, 2018, 10:55:19 AM
Charon is only about 1200 km in diameter. I'll be damned if that's a planet.

Also, I propose that betanin be renamed "beetyl juice".
Title: Re: Episode #688
Post by: gebobs on September 17, 2018, 11:00:25 AM
I'm sorry, but the 100 days ground zero fire bit from Science or Fiction is a bit too press-release-perfect for me. Ground zero had its own local weather for awhile. I was seeing and smelling this on my way to work every day after until some random day in November. Here's where the trouble begins. In my memory, the fire was declared out around THAT time — roughly 60 days later. I remember hearing it on either the radio or TV or both. I also remember the smell stopping around that time. I have no recollection of anyone discussing this in December 2001. More importantly, how does a fire know that a prominent base 10 number of days has passed?

Ground Zero stops burning, after 100 days
https://www.theguardian.com/world/2001/dec/20/september11.usa
Title: Re: Episode #688
Post by: seamas on September 17, 2018, 01:17:16 PM
I'm sorry, but the 100 days ground zero fire bit from Science or Fiction is a bit too press-release-perfect for me. Ground zero had its own local weather for awhile. I was seeing and smelling this on my way to work every day after until some random day in November. Here's where the trouble begins. In my memory, the fire was declared out around THAT time — roughly 60 days later. I remember hearing it on either the radio or TV or both. I also remember the smell stopping around that time. I have no recollection of anyone discussing this in December 2001. More importantly, how does a fire know that a prominent base 10 number of days has passed?

I recall the fires burning at least that long. I recall going downtown lose to the holidays, not far from the WTC and the area was still a wreck and you still saw smoke/steam  coming from the direction of the pile. My sister's husband was in the FDNY and had done a couple recovery visits to the pile over the months after the attack. Putting out flare-ups and whatnot and still dealing with smoldering fires below the surface of the pile was a very real problem that they had to have top-of mind at all times.


I thought this weeks SoF was the easiest. I mean the seeing eye dog was pure glurge, and the Nostradamus thing was believable because a lot of people were fact-checking crap their drunk uncles were forwarding..
I was surprised that the Rogues all thought America was unaware of Osama Bin Ladin and Al Queda at the time of the attacks. I mean before Noon on 9/11 there was no doubt it was a terrorist attack. Once the second plane hit, it was a forgone conclusion. Plus the WTC was attacked just years earlier.
Plus Al Queda and Bin Ladin were already well known for their Embassy bombings in the late '90s, plus other actions. iirc Bin Ladin was the subject of a 60 Minutes report in the late '90s.
Title: Re: Episode #688
Post by: PIgankle on September 17, 2018, 01:55:57 PM
FWIW - there wasn't even a dog named Daisy.  There were two seeing eye dogs who rescued their respective owners: Salty (partnered with Omar Rivera) and  Roselle (whose human, Michael Hingson, wrote a book currently on my bedside table.)
Title: Re: Episode #688
Post by: CarbShark on September 17, 2018, 02:28:05 PM
Below are links (crossposted) to Metzger's blog post and paper.

I think Steve is mischaracterizing Metzger's position. Metzger excludes satellites.

Plus, Metzger is not recommending that the IAU change its definition of planet. He's arguing that the IAU drop its definition of planet (which he argues is not scientific and is influenced by culture) and allow the scientific consensus on taxonomy develop following the scientific process as it does everywhere else in science, rather than top-down authority.


Below are links to Metzger's  blog post (where he provides the link to the paper) where he describes the issues pretty clearly.

Correction I stated a few times that only Pluto would be redefined as a planet by Metzger's definition, but Ceres, would be as well and few Kupier belt objects. But satellites (which orbit planets) would be excluded. I'm not sure if he considers Charon a satellite or not.



Debunking an Urban Legend of Asteroidal Proportions - Philip Metzger (https://www.philipmetzger.com/debunking-an-urban-legend-of-asteroidal-proportions/)

Quote
It gives a false view of how science operates and why taxonomy even exists in science. It was part of the rationale that was used to justify the IAU voting to redefine the term, planet, which made Pluto and Ceres into non-planets (that is, if we were submitting to the unscientific vote, which many of us are not).  This is all very harmful to science, not just because it propagates an urban legend in place of the truth, but because it gives the impression we make taxonomical decisions through authoritative bodies voting and imposing decisions on individual scientists. It gives the impression that science is supposed to be an authority-driven activity. It suggests that taxonomical categories are fairly arbitrary so voting is a decent way to decide them, or that we can shape them to fit  cultural expectations. “Culture wants a small number of big planets, and picking planet definitions is fairly arbitrary, so let’s just give culture what it wants!” Right? Wrong. That’s not science.




Preprint Asteroids-reclassified as non planets Metzger-et-al (https://www.philipmetzger.com/wp-content/uploads/2018/03/Preprint_Asteroids-reclassified-as-non-planets_Metzger-et-al.pdf)
Quote

We recommend that, regarding planetary taxonomy, central bodies such as the IAU do not resort to voting to create the illusion of scientific consensus. The IAU has done damage to the public perception of science as a process that is not dictated by a central authority, in its imposition of a definition of planet and the number of planets fitting that definition, which has been instilled in educational textbooks around the world on the basis of their authority. Rather than voting on any other taxonomical issues, the IAU should simply rescind its planetary (and dwarf planetary) definitions and not replace them with any new definitions. In short, the IAU should simply allow the scientific communities to reach consensus on taxonomies through precedent set in literature and conference proceedings. We further recommend that educational organizations teach students that taxonomy is a vital part of science, along with observing nature, forming hypotheses, and testing predictions. Scientists utilize taxonomy to organize their observations of nature, to enable clearer thinking, and to communicate concepts that they piece together into hypotheses. Therefore, definitions such as for planet are not determined arbitrarily nor to serve cultural purposes nor to fit culture’s preconceptions. The evolution of asteroid and planet taxonomy can be a pedagogical example of these concepts. We live in a time when the discovery of planetary bodies within our own solar system and around other stars is greatly expanding and revealing properties and solar system architectures not previously known or predicted. This will necessarily continue to drive the evolution of how we group objects into categories of planets and other taxons, motivated by scientific utility.

 
Title: Re: Episode #688
Post by: bachfiend on September 17, 2018, 08:17:33 PM
Below are links (crossposted) to Metzger's blog post and paper.

I think Steve is mischaracterizing Metzger's position. Metzger excludes satellites.

Plus, Metzger is not recommending that the IAU change its definition of planet. He's arguing that the IAU drop its definition of planet (which he argues is not scientific and is influenced by culture) and allow the scientific consensus on taxonomy develop following the scientific process as it does everywhere else in science, rather than top-down authority.


Below are links to Metzger's  blog post (where he provides the link to the paper) where he describes the issues pretty clearly.

Correction I stated a few times that only Pluto would be redefined as a planet by Metzger's definition, but Ceres, would be as well and few Kupier belt objects. But satellites (which orbit planets) would be excluded. I'm not sure if he considers Charon a satellite or not.



Debunking an Urban Legend of Asteroidal Proportions - Philip Metzger (https://www.philipmetzger.com/debunking-an-urban-legend-of-asteroidal-proportions/)

Quote
It gives a false view of how science operates and why taxonomy even exists in science. It was part of the rationale that was used to justify the IAU voting to redefine the term, planet, which made Pluto and Ceres into non-planets (that is, if we were submitting to the unscientific vote, which many of us are not).  This is all very harmful to science, not just because it propagates an urban legend in place of the truth, but because it gives the impression we make taxonomical decisions through authoritative bodies voting and imposing decisions on individual scientists. It gives the impression that science is supposed to be an authority-driven activity. It suggests that taxonomical categories are fairly arbitrary so voting is a decent way to decide them, or that we can shape them to fit  cultural expectations. “Culture wants a small number of big planets, and picking planet definitions is fairly arbitrary, so let’s just give culture what it wants!” Right? Wrong. That’s not science.




Preprint Asteroids-reclassified as non planets Metzger-et-al (https://www.philipmetzger.com/wp-content/uploads/2018/03/Preprint_Asteroids-reclassified-as-non-planets_Metzger-et-al.pdf)
Quote

We recommend that, regarding planetary taxonomy, central bodies such as the IAU do not resort to voting to create the illusion of scientific consensus. The IAU has done damage to the public perception of science as a process that is not dictated by a central authority, in its imposition of a definition of planet and the number of planets fitting that definition, which has been instilled in educational textbooks around the world on the basis of their authority. Rather than voting on any other taxonomical issues, the IAU should simply rescind its planetary (and dwarf planetary) definitions and not replace them with any new definitions. In short, the IAU should simply allow the scientific communities to reach consensus on taxonomies through precedent set in literature and conference proceedings. We further recommend that educational organizations teach students that taxonomy is a vital part of science, along with observing nature, forming hypotheses, and testing predictions. Scientists utilize taxonomy to organize their observations of nature, to enable clearer thinking, and to communicate concepts that they piece together into hypotheses. Therefore, definitions such as for planet are not determined arbitrarily nor to serve cultural purposes nor to fit culture’s preconceptions. The evolution of asteroid and planet taxonomy can be a pedagogical example of these concepts. We live in a time when the discovery of planetary bodies within our own solar system and around other stars is greatly expanding and revealing properties and solar system architectures not previously known or predicted. This will necessarily continue to drive the evolution of how we group objects into categories of planets and other taxons, motivated by scientific utility.

Steve Novella’s suggestion that the third criterion for defining a planet, that it’s cleared its orbit of other objects, is a sensible one, since it’s difficult to define what exactly ‘cleared’ means.  A planet being spherical and orbiting its star is pretty clear and easily applied.  Any body that’s orbiting its star and isn’t spherical isn’t a planet - it could be an asteroid or a comet.

It’s hardly likely to expand the category of solar planets to unmanageable proportions.

I think there’s still a problem with the definition of moons, as being anything that orbits a planet.  Perhaps moons should also be defined as bodies orbiting planets which are also large enough to be spherical too?    This would eliminate many of Jupiter’s 79 named moons as ‘moons.’  As well as Phobos and Deimos.  If humans manage to move an asteroid into Earth orbit, would that make it a ‘moon?’  I think not.

Steve’s definition of a moon as orbiting a planet with the centre of gravity of the combined system being within the planet (otherwise it’s a planetary pair) could break down occasionally.  What happens if the smaller body is orbiting in a very eccentric orbit?  When the  smaller body is at its apoapsis, the centre of gravity could well be outside the the larger body, in which case it’s a planetary pair.  But when the smaller body is at periapsis, the centre of gravity is within the larger body, so it’s now a planet and its moon.  So a body could swap from being a planet to being a moon in a single orbit.

And what is going to happen with the Earth-Moon system in the far distant future?  Could the Moon recede far enough that the centre of gravity is now outside the Earth - would that make the Moon into a planet then?
Title: Re: Episode #688
Post by: Alex Simmons on September 18, 2018, 02:22:12 AM
Currently the Earth and Moon are receding from each other. If the current rate is maintained then the Earth-Moon barycenter will begin to be outside the surface of the Earth after a few billion years. However the rate the pair recedes from each other is not a constant and there are many, many variables in play.
Title: Re: Episode #688
Post by: Tassie Dave on September 18, 2018, 04:26:29 AM
For the record, Bob is a philistine and Australian hamburgers don't have beets on them. They have beetroot which is lightly pickled and canned. It's not like we're pulling up the roots and slicing them to put directly on our burgers. I mean, some people might, but that's neither here nor there. IT'S BEETOOT AND IT'S DELICIOUS ON HAMBURGERS SO THERE.

I'm with Bob. Beetroot on a hamburger is horrible. Also I hate buying salad roles that have a slice of beetroot in it. It taints the whole roll  ???  >:(
Title: Re: Episode #688
Post by: CarbShark on September 18, 2018, 10:42:00 AM
Steve Novella’s suggestion that the third criterion for defining a planet, that it’s cleared its orbit of other objects, is a sensible one, since it’s difficult to define what exactly ‘cleared’ means. 

That’s not Steve suggestion, that’s the criteria that the IAU uses.

Are you agreeing that should be dropped?


Quote

A planet being spherical and orbiting its star is pretty clear and easily applied.  Any body that’s orbiting its star and isn’t spherical isn’t a planet - it could be an asteroid or a comet.

It’s hardly likely to expand the category of solar planets to unmanageable proportions.

There is no scientific reason to settle on a definition that keeps the number of planets small.

Quote
I think there’s still a problem with the definition of moons, as being anything that orbits a planet. 

A satellite is anything that orbits a planet.


Quote
Perhaps moons should also be defined as bodies orbiting planets which are also large enough to be spherical too?   

This would eliminate many of Jupiter’s 79 named moons as ‘moons.’  As well as Phobos and Deimos. 


What would be the scientific purpose of that?
Quote
If humans manage to move an asteroid into Earth orbit, would that make it a ‘moon?’  I think not.
Why not?


Quote
And what is going to happen with the Earth-Moon system in the far distant future?  Could the Moon recede far enough that the centre of gravity is now outside the Earth - would that make the Moon into a planet then?

As long as it’s still orbiting earth it’s a moon. If it recedes far enough that it no longer does then yes it becomes a planet.



Sent from my iPhone using Tapatalk
Title: Re: Episode #688
Post by: bachfiend on September 18, 2018, 03:36:43 PM
CarbShark,

Ceres was originally called a planet when it was discovered.  One of the reasons why it was downgraded was when other bodies were discovered at similar distances from the Sun, and if they were were called planets too, then the numbers of planets would soon assume very large numbers - so defining planets in such a way as to avoid unmanageable numbers made sense.

The same happened with Pluto.

Having a clear definition of a planet is important - it’s necessary for it to be large enough to be spherical. 

There should be a definition of planetary moons that excludes every tiny chunk of ice or rock, regardless of whether it’s metres or kilometres in maximum size, otherwise the number of moons will expand enormously.  Is there any point in listing (and naming) 79 moons of Jupiter, most of which are tiny?

You don’t seem to appreciate the situation with the Moon.  Currently the Moon is a moon.  But in a few billion years, it will become a planet.  If we every discover an almost identical twin of the Earth-Moon system orbiting another star, it doesn’t make much sense to call the Moon-twin a moon if it’s orbiting close to its planet and a planet if it’s orbiting a little further out.

And what would you call the moons if they were kicked out of their planetary orbits to orbit the Sun independently?  The Moon would be called a planet.  Many of the current Jovian moons, if it happened to them, would be called comets or asteroids.  The same with Phobos or Deimos.
Title: Re: Episode #688
Post by: Bytor on September 18, 2018, 08:41:14 PM
Light Sails

I wonder if any of the rogues I've ever read any Robert L. Forward? He was a hard SF Sutter with incredibly detailed explanations of the technology in his books (and he was also a physics professor). One of his books "Flight of the Dragonfly" is about a human mission to Barnards Star on a laser-propelled light sail vehicle.
Title: Re: Episode #688
Post by: CarbShark on September 18, 2018, 08:57:40 PM

Ceres was originally called a planet when it was discovered.  One of the reasons why it was downgraded was when other bodies were discovered at similar distances from the Sun, and if they were were called planets too, then the numbers of planets would soon assume very large numbers - so defining planets in such a way as to avoid unmanageable numbers made sense.

The same happened with Pluto.


This is astronomy. They deal with large numbers all the time. If they can manage 100+ Messier objects they can handle a couple dozen planets. (Not to mention the number of galaxies and stars)



Quote
Having a clear definition of a planet is important - it’s necessary for it to be large enough to be spherical. 

And directly orbits the sun (is not a satellite)

Quote

There should be a definition of planetary moons that excludes every tiny chunk of ice or rock, regardless of whether it’s metres or kilometres in maximum size, otherwise the number of moons will expand enormously.  Is there any point in listing (and naming) 79 moons of Jupiter, most of which are tiny?

In the taxonomy of Astronomy I don't think there's a separate criteria for moon and satellite. Moon is an informal way of saying satellite.

The Moon is the name of Earth's satellite. Whether or not there should be a different definition for satellites that are massive enough to be spherical is a separate issue.

Quote
You don’t seem to appreciate the situation with the Moon.  Currently the Moon is a moon.  But in a few billion years, it will become a planet.  If we every discover an almost identical twin of the Earth-Moon system orbiting another star, it doesn’t make much sense to call the Moon-twin a moon if it’s orbiting close to its planet and a planet if it’s orbiting a little further out.

Well, first, the fact that it has been receding does not mean it will forever. It may reach an equilibrium between its orbital speed and average distance.

Second, if it does continue to recede, until the time when it is no longer orbiting earth it will be a satellite. When it's not orbiting earth (and is directly orbiting the sun) it will be a planet.

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And what would you call the moons if they were kicked out of their planetary orbits to orbit the Sun independently? 
A planet, if they meet the criteria of a planet. An asteroid if they don't.
Quote
The Moon would be called a planet.  Many of the current Jovian moons, if it happened to them, would be called comets or asteroids.  The same with Phobos or Deimos.

None would be called comets. They are not comets. If they were directly orbiting the sun they would all be planets or asteroids.
Title: Re: Episode #688
Post by: The Latinist on September 18, 2018, 09:23:27 PM
Here’s the thing, though: it’s not really ever accurate to say that one object orbits another; always the two objects orbit the center of mass of their combined system (called its barycenter).  Depending on their respective masses, this can fall almost anywhere between the centers of the two objects.  For particularly lopsided relationships, that barycenter may lie inside one of the objects; but it’s a bit arbitrary to make that point the be-all-end-all of the definition of a moon. Indeed; it’s not really accurate to say that the Earth currently orbits the sun while the moon orbits the Earth; more accurately, they both orbit their barycenter and that barycenter orbits the sun.

So it’s not really a question of the Moon someday ceasing to orbit the Earth and beginning to orbit the sun.  Both the Earth and Moon will continue to orbit their barycenter, and that barycenter will drift toward the surface of the earth until it eventually no longer lies inside the Earth.  For a time it will be right at the surface, then it will move off into the atmosphere and eventually into space.  But both will always still orbit their barycenter, and that barycenter will continue to orbit the sun.
Title: Re: Episode #688
Post by: arthwollipot on September 18, 2018, 09:42:57 PM
more accurately, they both orbit their barycenter and that barycenter orbits the sun.

Even more accurately, that barycenter and the sun have a barycenter that both orbit.

Gravity is complicated.
Title: Episode #688
Post by: CarbShark on September 18, 2018, 09:52:45 PM
Add to that the  orbits are elliptical and in some cases can be influenced by other satellites and planets.

It is entirely possible for the moon to stop orbiting earth.

AFAIK, Pluto and Charon are the only case in the solar system where it’s not perfectly clear who’s orbiting whom, but even then the consensus is that Charon is a satellite.




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Title: Re: Episode #688
Post by: arthwollipot on September 18, 2018, 10:38:17 PM
Add to that the  orbits are elliptical and in some cases can be influenced by other satellites and planets.

If by "in some cases" you mean "always", then yes.

It is entirely possible for the moon to stop orbiting earth.

What?

AFAIK, Pluto and Charon are the only case in the solar system where it’s not perfectly clear who’s orbiting whom, but even then the consensus is that Charon is a satellite.

While this may be the case now, there is a probability that we will find other cases.
Title: Re: Episode #688
Post by: gebobs on September 19, 2018, 11:28:23 AM
How about make the criteria for a moon be if the barycenter lies outside a certain percentage of the distance between the centers of two objects. The Moon-Earth barycenter is about 98% of the distance between them. For Charon-Pluto, it's about 90%.
Title: Re: Episode #688
Post by: The Latinist on September 19, 2018, 01:24:40 PM
It is entirely possible for the moon to stop orbiting earth.

I'd love to hear you explain this further.
Title: Re: Episode #688
Post by: CarbShark on September 19, 2018, 01:29:16 PM
Add to that the  orbits are elliptical and in some cases can be influenced by other satellites and planets.

If by "in some cases" you mean "always", then yes.

Well, yes, but in some cases influenced enough to dynamically change the orbits.
Quote

It is entirely possible for the moon to stop orbiting earth.

What?

If the Moon keeps receding eventually it will be far enough away at its apogee that the gravitational attraction to Earth would be less than the pull of the Sun, or Venus, or even Mars or Jupiter. If that were to happen the Moon could be captured by the Sun, another planet or could even be expelled from the solar system.


Quote
AFAIK, Pluto and Charon are the only case in the solar system where it’s not perfectly clear who’s orbiting whom, but even then the consensus is that Charon is a satellite.

While this may be the case now, there is a probability that we will find other cases.

Sure, and if and when that happens we (astronomers) would make a determination as to which, if either, would be considered a satellite.

But if they're roughly equal in size then I imagine that they would both be considered planets.

Again, how is that a problem for science?

It's only what Metzger considers "Cultural" considerations that make people uncomfortable with, say, dozens of planets, and are the motive for coming up with definitions that limit the number.

There's no scientific reason to limit the number of planets.

(I was neutral on this question until I found Metzger's blog and the full text of the paper. At this point I agree with Metzger.)
Title: Re: Episode #688
Post by: CarbShark on September 19, 2018, 01:32:10 PM
How about make the criteria for a moon be if the barycenter lies outside a certain percentage of the distance between the centers of two objects. 

Why?

What's the scientific reason and purpose for introducing this arbitrary criteria?
Title: Re: Episode #688
Post by: 2397 on September 19, 2018, 01:46:33 PM
Listening to the planet segment, I agree with Bob for the most part. Because he brings up the things I was thinking of. Such as doesn't a planet's ability to gravitate itself into a sphere depend on what it's made of?

In a way, Titan and Ganymede are more like planets than Saturn and Jupiter are, if planets are something broadly similar to Earth. I was fine with Pluto not being a planet, it doesn't seem to fit among the rest, although it could be argued it's on the other extreme where Earth is somewhere in the middle.

A definition of planets that includes Charon and Jupiter, but not the largest moons, there is something about that that doesn't seem right to me.
Title: Re: Episode #688
Post by: The Latinist on September 19, 2018, 01:59:28 PM
Here's another wrinkle: the barycenter of the Sun-Jupiter system is actually outside the radius of the sun.  Should we call Jupiter something other than a planet?

If the Moon keeps receding eventually it will be far enough away at its apogee that the gravitational attraction to Earth would be less than the pull of the Sun, or Venus, or even Mars or Jupiter. If that were to happen the Moon could be captured by the Sun, another planet or could even be expelled from the solar system.

The sun has already 'captured' the moon in the sense that it and the earth both orbit the sun.  The question is whether the moon can cease to orbit the earth, which is entirely a function of its orbital distance and its velocity relative to earth, and I'm pretty sure (though it's been a long time since I read about it in detail) that the earth and moon will become doubly-tidally-locked before the moon reaches escape velocity for its orbital distance from the earth.  At that point the moon will cease to recede, and we will be stuck together.

So, no, it's not possible, barring some sort of solar-system transforming collision with another star, for the moon to stop orbiting the Earth.
Title: Re: Episode #688
Post by: CarbShark on September 19, 2018, 02:39:48 PM
Here's another wrinkle: the barycenter of the Sun-Jupiter system is actually outside the radius of the sun.  Should we call Jupiter something other than a planet?

If the Moon keeps receding eventually it will be far enough away at its apogee that the gravitational attraction to Earth would be less than the pull of the Sun, or Venus, or even Mars or Jupiter. If that were to happen the Moon could be captured by the Sun, another planet or could even be expelled from the solar system.

The sun has already 'captured' the moon in the sense that it and the earth both orbit the sun.  The question is whether the moon can cease to orbit the earth, which is entirely a function of its orbital distance and its velocity relative to earth, and I'm pretty sure (though it's been a long time since I read about it in detail) that the earth and moon will become doubly-tidally-locked before the moon reaches escape velocity for its orbital distance from the earth.  At that point the moon will cease to recede, and we will be stuck together.

So, no, it's not possible, barring some sort of solar-system transforming collision with another star, for the moon to stop orbiting the Earth.

Capturing the Moon would entail having a stronger pull on it directly than the earth does. This could have the effect of preventing it's return from apogee or increasing its speed significantly on approach to perigee. Either could send it on a different trajectory. If this happened the most likely trajectory would be new orbit around the sun. Other trajectories could slingshot it out of the solar system; put it into orbit around venus, say, or even crash it into the sun or the earth.

To say it's "not possible" is false, but I agree it's not likely.
Title: Re: Episode #688
Post by: The Latinist on September 19, 2018, 02:59:45 PM
Dude, the sun already has significantly
Here's another wrinkle: the barycenter of the Sun-Jupiter system is actually outside the radius of the sun.  Should we call Jupiter something other than a planet?

If the Moon keeps receding eventually it will be far enough away at its apogee that the gravitational attraction to Earth would be less than the pull of the Sun, or Venus, or even Mars or Jupiter. If that were to happen the Moon could be captured by the Sun, another planet or could even be expelled from the solar system.

The sun has already 'captured' the moon in the sense that it and the earth both orbit the sun.  The question is whether the moon can cease to orbit the earth, which is entirely a function of its orbital distance and its velocity relative to earth, and I'm pretty sure (though it's been a long time since I read about it in detail) that the earth and moon will become doubly-tidally-locked before the moon reaches escape velocity for its orbital distance from the earth.  At that point the moon will cease to recede, and we will be stuck together.

So, no, it's not possible, barring some sort of solar-system transforming collision with another star, for the moon to stop orbiting the Earth.

Capturing the Moon would entail having a stronger pull on it directly than the earth does. This could have the effect of preventing it's return from apogee or increasing its speed significantly on approach to perigee. Either could send it on a different trajectory. If this happened the most likely trajectory would be new orbit around the sun. Other trajectories could slingshot it out of the solar system; put it into orbit around venus, say, or even crash it into the sun or the earth.

To say it's "not possible" is false, but I agree it's not likely.

That’s not how it works.  The earth and the moon are gravitationally bound.  As long as that is true, the pull of the sun acts as though it is pulling on the barycenter of the earth-moon system, and any changes in the effects of the sun are felt by the system; they cannot be felt more by the moon than by the earth—the two will accelerate or decelerate as a pair.  The sun can’t just reach out and touch only the moon.

The only way for that to change is for the moon to achieve escape velocity, and that’s not something the sun can impart to it.  It just isn’t.

Incidentally, the sun’s pull on the moon already exceeds that of the earth by more than double.  But that’s irrelevant to it pulling the two apart because *all* that matters is the relative velocities ofbthe two bodies, and there’s no way for the sun to differentially accelerate the moon as long as it’s gravitationally bound to the earth.  And the recession of of the moon due to tidal forces is just not adequate for it to achieve escape velocity before tidal locking.  Barring, as I said, a colission or something else from *outside* the earth-moon-sun system that can impart new velocity to the moon, it simply cannot escape the earth.
Title: Re: Episode #688
Post by: tralfaz on September 19, 2018, 03:30:59 PM
Beets.  Oxalic acid.  I guess I'm the only one here who prepares beets and the beet greens.
Title: Re: Episode #688
Post by: CarbShark on September 19, 2018, 03:35:21 PM
Dude, the sun already has significantly
Here's another wrinkle: the barycenter of the Sun-Jupiter system is actually outside the radius of the sun.  Should we call Jupiter something other than a planet?

If the Moon keeps receding eventually it will be far enough away at its apogee that the gravitational attraction to Earth would be less than the pull of the Sun, or Venus, or even Mars or Jupiter. If that were to happen the Moon could be captured by the Sun, another planet or could even be expelled from the solar system.

The sun has already 'captured' the moon in the sense that it and the earth both orbit the sun.  The question is whether the moon can cease to orbit the earth, which is entirely a function of its orbital distance and its velocity relative to earth, and I'm pretty sure (though it's been a long time since I read about it in detail) that the earth and moon will become doubly-tidally-locked before the moon reaches escape velocity for its orbital distance from the earth.  At that point the moon will cease to recede, and we will be stuck together.

So, no, it's not possible, barring some sort of solar-system transforming collision with another star, for the moon to stop orbiting the Earth.

Capturing the Moon would entail having a stronger pull on it directly than the earth does. This could have the effect of preventing it's return from apogee or increasing its speed significantly on approach to perigee. Either could send it on a different trajectory. If this happened the most likely trajectory would be new orbit around the sun. Other trajectories could slingshot it out of the solar system; put it into orbit around venus, say, or even crash it into the sun or the earth.

To say it's "not possible" is false, but I agree it's not likely.

That’s not how it works.  The earth and the moon are gravitationally bound.  As long as that is true, the pull of the sun acts as though it is pulling on the barycenter of the earth-moon system, and any changes in the effects of the sun are felt by the system; they cannot be felt more by the moon than by the earth—the two will accelerate or decelerate as a pair.  The sun can’t just reach out and touch only the moon.

So you're saying that in a scenario when the moon is approaching apogee (moving away from Earth) and Earth is moving away from the sun and the moon is significantly closer to the sun than the earth (because the two have been receding for x number of years) that the sun would have not have a significantly increased gravitational attraction to the moon than the earth?

I think that's exactly how it works.

Quote


Incidentally, the sun’s pull on the moon already exceeds that of the earth by more than double.

Sure but we're talking about a scenario where those relative gravitational forces change.

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  But that’s irrelevant to it pulling the two apart because *all* that matters is the relative velocities ofbthe two bodies, and there’s no way for the sun to differentially accelerate the moon as long as it’s gravitationally bound to the earth. 
As the moon continues receeding then eventually the gravitational attraction to earth becomes weaker and weaker. There are times in their orbits that the Earth is moving away from the Sun and the Moon is moving toward the Sun and is closer to the sun than the Earth is.
 


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And the recession of of the moon due to tidal forces is just not adequate for it to achieve escape velocity before tidal locking.  Barring, as I said, a colission or something else from *outside* the earth-moon-sun system that can impart new velocity to the moon, it simply cannot escape the earth.

Again, I do not think this is likely. As I said before the Moon will probably not continue to recede indefinitely. But if it did, then yes, the Moon could stop orbiting the earth.

Title: Re: Episode #688
Post by: Alex Simmons on September 19, 2018, 05:01:22 PM
If the Moon keeps receding eventually it will be far enough away at its apogee that the gravitational attraction to Earth would be less than the pull of the Sun, or Venus, or even Mars or Jupiter. If that were to happen the Moon could be captured by the Sun, another planet or could even be expelled from the solar system.
No.

Let's assume that the Sun won't vapourise the Earth-Moon system during it's red giant phase in about 5 billion years or so from now.

Moon and Earth are currently receding from each other however that won't continue forever. It only happens while there is a tidal energy "swap" going on. Eventually the Earth will also become tidally locked to the Moon and the Earth and Moon will no longer be receding from each other. Indeed the earth-Moon orbit will likely begin to decay again as the Earth-Moon orbital energy is slowly leaked to the Sun via tidal force swaps. We are talking something like 50 billion years into the future. Given another 10-20 billion years and the orbital decay may mean a collision or Roche limit reached.

But there is also the possibility that before then, during the Sun's red giant phase orbital drag due to Sun's atmosphere will cause the Moon's orbit to decay more quickly, possibly even to the point of reaching the Roche limit resulting in the destruction of the Moon.

The Moon is not going to leave Earth orbit.

As for other planets, the gradual loss of mass by the Sun will see the planet's orbit expand making planetary interactions weaker, not stronger.

About the only thing to fling something out of the Solar system would be a very close encounter with another star or hot jupiter.
Title: Re: Episode #688
Post by: The Latinist on September 19, 2018, 05:13:32 PM
No, Ed, you’re just making shit up.  Unless the sun can impart velocity to the moon such that it exceeds escape velocity, it simply cannot pull the moon out of earth orbit.  And it cannot do that.  Not “is very unlikely to,” but “cannot.”  You’re talking about this like it’s some sort of chaotic system that can’t be predicted when it’s actually some of the best-understood and mechanistic physics in the universe.
Title: Re: Episode #688
Post by: Alex Simmons on September 19, 2018, 06:17:43 PM
Beets.  Oxalic acid.  I guess I'm the only one here who prepares beets and the beet greens.
Many years ago when I was still racing I used beet juice in a self trial for exploring its potential ergogenic effects. Red pee and poo were certainly novel experiences during the experiment.

Dietary nitrates have been researched quite a bit since then and have been shown to be good for heart health and do have a positive influence on athletic aerobic capability.
Title: Re: Episode #688
Post by: Alex Simmons on September 19, 2018, 06:57:14 PM
No, Ed, you’re just making shit up.  Unless the sun can impart velocity to the moon such that it exceeds escape velocity, it simply cannot pull the moon out of earth orbit.  And it cannot do that.  Not “is very unlikely to,” but “cannot.”  You’re talking about this like it’s some sort of chaotic system that can’t be predicted when it’s actually some of the best-understood and mechanistic physics in the universe.
Yup

The escape velocity from Earth's gravitational well is √2 times the Moon's actual velocity.

This ratio applies to any object orbiting another. e.g. Earth's escape velocity from the Sun is √2 times the Earth's orbital velocity.

Hence it ain't leaving since as you say there is nothing to increase the Moon's velocity (relative to Earth). Only a very close encounter from a large extra solar visitor could do that.
Title: Re: Episode #688
Post by: brilligtove on September 19, 2018, 07:15:56 PM
Well, I'm sure a direct hit from a rogue planet travelling through our solar system would do it.

Oh wait. That would be more of an 'essploderationistic' interaction, now wouldn't it. :)
Title: Re: Episode #688
Post by: CarbShark on September 19, 2018, 07:18:01 PM
No, Ed, you’re just making shit up.  Unless the sun can impart velocity to the moon such that it exceeds escape velocity, it simply cannot pull the moon out of earth orbit.  And it cannot do that.  Not “is very unlikely to,” but “cannot.”  You’re talking about this like it’s some sort of chaotic system that can’t be predicted when it’s actually some of the best-understood and mechanistic physics in the universe.
Yup

The escape velocity from Earth's gravitational well is √2 times the Moon's actual velocity.

This ratio applies to any object orbiting another. e.g. Earth's escape velocity from the Sun is √2 times the Earth's orbital velocity.

Hence it ain't leaving since as you say there is nothing to increase the Moon's velocity (relative to Earth). Only a very close encounter from a large extra solar visitor could do that.

Once again, this entire discussion is based on the proposition someone else suggested (bachfiend?) that the Moon would continue to recede from the Earth.

I said that probably would not happen (and I agree that without some outside force, it will not happen).

But, if that were to happen, if the Moon were to steadily recede from it's orbit gradually increasing its distance from the Earth, then yes, the Moon could be pulled away from the Earth. Actually, if the Moon (or any satellite) steadily increased its distance from the planet it orbits it would be inevitable that it would leave its orbit.

And if the Moon ever did so, then yes it would be classified as a planet if it orbited the Sun, or if it were ejected from the solar system.

It would be considered a satellite if it were captured by Venus.

It would not be considered an asteroid.



Title: Re: Episode #688
Post by: arthwollipot on September 19, 2018, 09:10:46 PM
Add to that the  orbits are elliptical and in some cases can be influenced by other satellites and planets.

If by "in some cases" you mean "always", then yes.

Well, yes, but in some cases influenced enough to dynamically change the orbits.

No - in all cases, an object's orbit is influenced by the gravitational fields of other objects in space. That's how Neptune was discovered - because its precence was altering Uranus' orbit. Technically every object in space is feeling a gravitational influence from every other object in the universe but beyond a certain distance these influences are miniscule enough to be ignored for most practical purposes.
Title: Re: Episode #688
Post by: The Latinist on September 19, 2018, 10:16:10 PM
To be constitutionally incapable of admitting when one is wrong, as you have proved yourself over and over again, is incompatible with skepticism, CarbShark. It’s okay: everyone’s wrong sometimes, and this is one of your times.  Just admit that you didn’t know what you were talking about and move on. Perhaps even grow a little humbler because of the experience.
Title: Re: Episode #688
Post by: CarbShark on September 19, 2018, 11:56:56 PM
Go back and follow the conversation from the start. Someone else suggested that the moon would keep receding  from earth until, oh no, it became a planet

I said from the start that wouldn’t happen, but if it did continue to recede then yes it would stop being a satellite and start being a planet.

You have ignored that I was responding to a hypothetical and, probably because you hold a grudge over some past discussion, you’ve ignored my repeated disclaimers (how skeptical is that?)

I fully admit when I make mistakes and have whenever appropriate. In this case given the hypothetical of the moon continuing to proceed away from earth it’s a certainty it would eventually stop orbiting earth and get captured by the sun, or another planet or ejected from the solar system. Or collide with earth or something else.

But, as I’ve said repeatedly now, that’s not going to happen.


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Title: Re: Episode #688
Post by: bachfiend on September 20, 2018, 01:00:43 AM
Go back and follow the conversation from the start. Someone else suggested that the moon would keep receding  from earth until, oh no, it became a planet

I said from the start that wouldn’t happen, but if it did continue to recede then yes it would stop being a satellite and start being a planet.

You have ignored that I was responding to a hypothetical and, probably because you hold a grudge over some past discussion, you’ve ignored my repeated disclaimers (how skeptical is that?)

I fully admit when I make mistakes and have whenever appropriate. In this case given the hypothetical of the moon continuing to proceed away from earth it’s a certainty it would eventually stop orbiting earth and get captured by the sun, or another planet or ejected from the solar system. Or collide with earth or something else.

But, as I’ve said repeatedly now, that’s not going to happen.


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The Moon will continue to recede from the Earth until the Earth becomes tidally locked to the Moon, which (as has been noted) will happen in around 60 billion years, considerably longer than the life expectancy of the solar system.

Basically, the Earth produces a bulge on the Moon on the side facing it.  As does the Moon produce a bulge on the Earth on the side facing it.  The Earth currently rotates once in around 24 hours and the Moon orbits the Earth once in around 28 days.  The Moon pulls on the bulge on the Earth slowing down the Earth’s rotation, so that the length of an Earth day increases.  The Earth pulls on the bulge in the Moon causing its orbital speed to increase.  So the Moon must continue to recede, until the bulge on the Earth stops rotating faster than the orbiting Moon and remains directly beneath the Moon all the time (ie the Earth is tidally locked).

The argument isn’t whether the Moon is a moon or a planet if it’s ejected.  It’s how the Moon could be a moon now, and then suddenly become a planet in a planetary pair when it has receded sufficiently.
Title: Re: Episode #688
Post by: CarbShark on September 20, 2018, 02:15:29 AM
Go back and follow the conversation from the start. Someone else suggested that the moon would keep receding  from earth until, oh no, it became a planet

I said from the start that wouldn’t happen, but if it did continue to recede then yes it would stop being a satellite and start being a planet.

You have ignored that I was responding to a hypothetical and, probably because you hold a grudge over some past discussion, you’ve ignored my repeated disclaimers (how skeptical is that?)

I fully admit when I make mistakes and have whenever appropriate. In this case given the hypothetical of the moon continuing to proceed away from earth it’s a certainty it would eventually stop orbiting earth and get captured by the sun, or another planet or ejected from the solar system. Or collide with earth or something else.

But, as I’ve said repeatedly now, that’s not going to happen.


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The Moon will continue to recede from the Earth until the Earth becomes tidally locked to the Moon, which (as has been noted) will happen in around 60 billion years, considerably longer than the life expectancy of the solar system.

Basically, the Earth produces a bulge on the Moon on the side facing it.  As does the Moon produce a bulge on the Earth on the side facing it.  The Earth currently rotates once in around 24 hours and the Moon orbits the Earth once in around 28 days.  The Moon pulls on the bulge on the Earth slowing down the Earth’s rotation, so that the length of an Earth day increases.  The Earth pulls on the bulge in the Moon causing its orbital speed to increase.  So the Moon must continue to recede, until the bulge on the Earth stops rotating faster than the orbiting Moon and remains directly beneath the Moon all the time (ie the Earth is tidally locked).
Nice summary of the wiki page.
Quote

The argument isn’t whether the Moon is a moon or a planet if it’s ejected.  It’s how the Moon could be a moon now, and then suddenly become a planet in a planetary pair when it has receded sufficiently.

Here’s the thing, neither Metzger nor the IAU agree with you.

By both definitions, if the Moon were orbiting the Sun and not the Earth it would be a planet. But for as long as it’s orbiting Earth it’s a satellite.

Same for a good number of other satellites in the solar system.

But, by the IAU definition, they would not be considered planets if there were asteroids and dust in their orbits, sort of.

That would change them from planets to dwarf planets.

I think that makes less sense. Particularly since the size of the object is not part of the criteria as long as it’s big enough to be a sphere.




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Title: Re: Episode #688
Post by: gebobs on September 20, 2018, 09:21:05 AM
How about make the criteria for a moon be if the barycenter lies outside a certain percentage of the distance between the centers of two objects. 

Why?

What's the scientific reason and purpose for introducing this arbitrary criteria?

Fark if I know. What's the scientific reason for the criteria being that the barycenter be within the radius of one of the bodies? Is that any less arbitrary?
Title: Re: Episode #688
Post by: brilligtove on September 20, 2018, 10:22:02 AM
It is less arbitrary in that it is an intrinsic property of the bodies in the system, and not a tuned multiplier of that property.

I'd go with this:

| Gravitational
| Sphere
|
| Orbits
| Star
|
| Orbits Planet
| Barycentre in
| planet
| Orbits Planet
| Barycentre in
| space
|---------------|---------------|---------------|---------------|---------------
| Asteroid: | no| yes | no | no
| Moon:    | n/a | no | yes | no
| Planet:   | yes | yes | no* | yes*

*Ignore if the body orbits the sun only and has no satellites.
Title: Re: Episode #688
Post by: CarbShark on September 20, 2018, 11:29:11 AM
It is less arbitrary in that it is an intrinsic property of the bodies in the system, and not a tuned multiplier of that property.

I'd go with this:

| Gravitational
| Sphere
|
| Orbits
| Star
|
| Orbits Planet
| Barycentre in
| planet
| Orbits Planet
| Barycentre in
| space
|---------------|---------------|---------------|---------------|---------------
| Asteroid: | no| yes | no | no
| Moon:    | n/a | no | yes | no
| Planet:   | yes | yes | no* | yes*

*Ignore if the body orbits the sun only and has no satellites.

Again, what is the scientific purpose of these criteria? What makes it better than simply establishing that if they orbit each other it's a planet/satellite?

Are you dropping the definition of Dwarf Planet?

Jupiter is a planet, right? But the barycenter between Jupiter and the Sun is in space.

If that aspect changes the definition of whether an object is a satellite or a planet shouldn't that also change the definition of whether an object is a planet or something else?

Also, why using the term "moon" rather than satellite (or natural satellite)?

By this definition Ceres would be a planet?

By this definition, Pluto/Charon would be double planets?

By this definition Earth/Moon would become double planets when the moon recedes far enough that the barycenter is in space?

But here's the thing, all this discussion about what the definition of planet should be is exactly what Metzger wants, and is exactly why he's critical of the IAU.

The criteria should be handled via science and the scientific method and a consensus should evolve as these questions are studied and answered by scientists working in the field (astronomers) and publishing in peer review journals, etc.

What the IAU has done is issued a top down, authoritative criteria and definition which some argue (in this very thread) should end this discussion and only "malcontents" or outliers on the "fringe" dispute.

That's not scientific. That's not science.

Title: Re: Episode #688
Post by: bachfiend on September 20, 2018, 03:53:01 PM
It is less arbitrary in that it is an intrinsic property of the bodies in the system, and not a tuned multiplier of that property.

I'd go with this:

| Gravitational
| Sphere
|
| Orbits
| Star
|
| Orbits Planet
| Barycentre in
| planet
| Orbits Planet
| Barycentre in
| space
|---------------|---------------|---------------|---------------|---------------
| Asteroid: | no| yes | no | no
| Moon:    | n/a | no | yes | no
| Planet:   | yes | yes | no* | yes*

*Ignore if the body orbits the sun only and has no satellites.

Again, what is the scientific purpose of these criteria? What makes it better than simply establishing that if they orbit each other it's a planet/satellite?

Are you dropping the definition of Dwarf Planet?

Jupiter is a planet, right? But the barycenter between Jupiter and the Sun is in space.

If that aspect changes the definition of whether an object is a satellite or a planet shouldn't that also change the definition of whether an object is a planet or something else?

Also, why using the term "moon" rather than satellite (or natural satellite)?

By this definition Ceres would be a planet?

By this definition, Pluto/Charon would be double planets?

By this definition Earth/Moon would become double planets when the moon recedes far enough that the barycenter is in space?

But here's the thing, all this discussion about what the definition of planet should be is exactly what Metzger wants, and is exactly why he's critical of the IAU.

The criteria should be handled via science and the scientific method and a consensus should evolve as these questions are studied and answered by scientists working in the field (astronomers) and publishing in peer review journals, etc.

What the IAU has done is issued a top down, authoritative criteria and definition which some argue (in this very thread) should end this discussion and only "malcontents" or outliers on the "fringe" dispute.

That's not scientific. That's not science.

Before went down this rabbit hole of whether the Moon is a moon or a planet in some far distant time, the point I was making was there should be more strict definitions as to what a planetary moon is.  Jupiter currently has 79 named (or at least numbered) moons, most of which are tiny, consisting of irregular lumps of ice and/or rock.  The number undoubtedly will increase in the future.

I think it would be reasonable to restrict the term planetary moons to bodies large enough to be spherical orbiting planets.  Anything smaller, captured irregular chunks of stone and/or ice would get some other designation.

‘Moon’ should be restricted to bodies large enough to be spherical and which would otherwise be called a planet.  I don’t have any problem in accepting Ceres as a planet, if the criterion of a planet changes to it being large enough to be spherical.  A planet need not be orbiting a star anyway.  Rogue planets, of which there are probably a larger number than planets orbiting stars, don’t orbit stars.

Newly discovered bodies should be required to ‘prove’ their status as moons or planets by being large enough to be spherical.  Until then they should just be a number.  Extrasolar planets are reasonably easy to define currently.  Anything orbiting a far distant star large enough to cause a wobble in the star or occlude a detectable fraction of its light is large enough to be a planet.

Title: Re: Episode #688
Post by: The Latinist on September 20, 2018, 04:37:38 PM
I strongly disagree that there is a reason to differentiate a “moon” from any other natural satellite based upon a criterion of sphericity.
Title: Re: Episode #688
Post by: CarbShark on September 20, 2018, 05:21:09 PM
Before went down this rabbit hole of whether the Moon is a moon or a planet in some far distant time, the point I was making was there should be more strict definitions as to what a planetary moon is.  Jupiter currently has 79 named (or at least numbered) moons, most of which are tiny, consisting of irregular lumps of ice and/or rock.  The number undoubtedly will increase in the future.

I think it would be reasonable to restrict the term planetary moons to bodies large enough to be spherical orbiting planets.  Anything smaller, captured irregular chunks of stone and/or ice would get some other designation.

‘Moon’ should be restricted to bodies large enough to be spherical and which would otherwise be called a planet.  I don’t have any problem in accepting Ceres as a planet, if the criterion of a planet changes to it being large enough to be spherical. 

Satellites. Not "moons," satellites. Jupiter has 79 satellites. If you're going to discuss scientific taxonomy, you should probably use the taxonomy of the field.

Is 79 too many? What's the correct and reasonable number? 42?

What number of planets will you settle for? 9? 10? A bakers dozen?

We would need to know those numbers in advance in order to devise a criteria for scientists to use to define these objects that results in number of them that doesn't overwhelm you with too many.

Are you comfortable with the number of comets or should we change that definition too?

Also, too many stars?

Quote
A planet need not be orbiting a star anyway.  Rogue planets, of which there are probably a larger number than planets orbiting stars, don’t orbit stars.

Newly discovered bodies should be required to ‘prove’ their status as moons or planets by being large enough to be spherical.  Until then they should just be a number.  Extrasolar planets are reasonably easy to define currently.  Anything orbiting a far distant star large enough to cause a wobble in the star or occlude a detectable fraction of its light is large enough to be a planet.

Well, they may look like a planet and they may act like a planet, but the IAU only considers spherical objects orbiting the Sun and that have cleared their own orbits to be planets.


Pluto and the Solar System | IAU (https://www.iau.org/public/themes/pluto/)


Quote
A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

Those others are exoplanets or rogue planets. Not planets. Which is just as well, because there seem to be a large number of those, too. And I bet a lot of them have a lot of satellites too.
Title: Re: Episode #688
Post by: brilligtove on September 20, 2018, 05:54:27 PM
It is less arbitrary in that it is an intrinsic property of the bodies in the system, and not a tuned multiplier of that property.

I'd go with this:

| Gravitational
| Sphere
|
| Orbits
| Star
|
| Orbits Planet
| Barycentre in
| planet
| Orbits Planet
| Barycentre in
| space
|---------------|---------------|---------------|---------------|---------------
| Asteroid: | no| yes | no | no
| Moon:    | n/a | no | yes | no
| Planet:   | yes | yes | no* | yes*

*Ignore if the body orbits the sun only and has no satellites.

Again, what is the scientific purpose of these criteria? What makes it better than simply establishing that if they orbit each other it's a planet/satellite?

Are you dropping the definition of Dwarf Planet?

Jupiter is a planet, right? But the barycenter between Jupiter and the Sun is in space.

If that aspect changes the definition of whether an object is a satellite or a planet shouldn't that also change the definition of whether an object is a planet or something else?

Also, why using the term "moon" rather than satellite (or natural satellite)?

By this definition Ceres would be a planet?

By this definition, Pluto/Charon would be double planets?

By this definition Earth/Moon would become double planets when the moon recedes far enough that the barycenter is in space?

But here's the thing, all this discussion about what the definition of planet should be is exactly what Metzger wants, and is exactly why he's critical of the IAU.

The criteria should be handled via science and the scientific method and a consensus should evolve as these questions are studied and answered by scientists working in the field (astronomers) and publishing in peer review journals, etc.

What the IAU has done is issued a top down, authoritative criteria and definition which some argue (in this very thread) should end this discussion and only "malcontents" or outliers on the "fringe" dispute.

That's not scientific. That's not science.



I liked Steve's suggestion overall, and put it into a table. I have no predetermined numbers of anything in mind. The barycentrer of opbjucts orbiting the sun is not a factor in my definition of planet. Being a sphere orbiting the sun is. A sattellite orbiting a planet is usually called a moon, so Icalled them moons. But satellite is fine. To be a satellite the barycentre of the system is beneath the surface of a planet. If the barycentre is in space between a planet and what would otherwise be a satellite, it's a binary planet.

I suppose some additional qualifcations  are needed for planet to distinguish it from binary stars, star+neutraon star, star+black hole, and so on.

I like the idea that the scientific community should come to consensus on taxonomy like this. Ithink the IAU could provide a valuable service by doumenting that kind of consensus.
Title: Re: Episode #688
Post by: bachfiend on September 20, 2018, 08:20:27 PM
Before went down this rabbit hole of whether the Moon is a moon or a planet in some far distant time, the point I was making was there should be more strict definitions as to what a planetary moon is.  Jupiter currently has 79 named (or at least numbered) moons, most of which are tiny, consisting of irregular lumps of ice and/or rock.  The number undoubtedly will increase in the future.

I think it would be reasonable to restrict the term planetary moons to bodies large enough to be spherical orbiting planets.  Anything smaller, captured irregular chunks of stone and/or ice would get some other designation.

‘Moon’ should be restricted to bodies large enough to be spherical and which would otherwise be called a planet.  I don’t have any problem in accepting Ceres as a planet, if the criterion of a planet changes to it being large enough to be spherical. 

Satellites. Not "moons," satellites. Jupiter has 79 satellites. If you're going to discuss scientific taxonomy, you should probably use the taxonomy of the field.

Is 79 too many? What's the correct and reasonable number? 42?

What number of planets will you settle for? 9? 10? A bakers dozen?

We would need to know those numbers in advance in order to devise a criteria for scientists to use to define these objects that results in number of them that doesn't overwhelm you with too many.

Are you comfortable with the number of comets or should we change that definition too?

Also, too many stars?

Quote
A planet need not be orbiting a star anyway.  Rogue planets, of which there are probably a larger number than planets orbiting stars, don’t orbit stars.

Newly discovered bodies should be required to ‘prove’ their status as moons or planets by being large enough to be spherical.  Until then they should just be a number.  Extrasolar planets are reasonably easy to define currently.  Anything orbiting a far distant star large enough to cause a wobble in the star or occlude a detectable fraction of its light is large enough to be a planet.

Well, they may look like a planet and they may act like a planet, but the IAU only considers spherical objects orbiting the Sun and that have cleared their own orbits to be planets.


Pluto and the Solar System | IAU (https://www.iau.org/public/themes/pluto/)


Quote
A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

Those others are exoplanets or rogue planets. Not planets. Which is just as well, because there seem to be a large number of those, too. And I bet a lot of them have a lot of satellites too.

‘Moon’ is a perfectly acceptable term for bodies orbiting planets.  NASA also uses the term ‘natural satellites’ (not just ‘satellites’ to label ‘moons’, and to distinguish them from artificial satellites, such as the ISS).  There are hundreds of identified ‘moons’ in the solar system, including moons orbiting asteroids.

Ceres was originally called a planet when it was discovered, but it was downgraded to an asteroid when further bodies were discovered in the asteroid belt, and it was feared that the number of planets would swell into the hundreds.  I don’t have any problems in accepting that Ceres is a planet, as is too Pluto and Charon, if that’s eventually what is decided.  I think that it would be reasonable to call any body large enough to be spherical orbiting a star a planet.  Any body large enough to be spherical orbiting a planet is a moon.

Whether a body is spherical or not is a pretty clear dividing line, removing the need to make arbitrary determinations, such as whether a large mass of ice orbiting within Saturn’s rings is a ‘moon’ or a ‘moonlet.’

Anything not fulfilling these pretty basic and easily applied definitions should have a different name.  Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’  And stop worrying about arguments about how it came to be formed, whether it was captured by the planet from elsewhere, remnants of the planetary formation, or debris from subsequent collisions.
Title: Re: Episode #688
Post by: CarbShark on September 20, 2018, 08:53:52 PM
Anything not fulfilling these pretty basic and easily applied definitions should have a different name. 

If that would be helpful for astronomers they'd probably do that. But the overwhelming consensus is that a satellite is a satellite and size and shape doesn't matter.

Quote
Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’   

All of these terms are "historical." Planet used to describe "wandering star" because the planets wandered in unpredictable ways across the night sky.

Comet was used to describe a "hairy star"

 

Title: Re: Episode #688
Post by: bachfiend on September 20, 2018, 10:11:42 PM
Anything not fulfilling these pretty basic and easily applied definitions should have a different name. 

If that would be helpful for astronomers they'd probably do that. But the overwhelming consensus is that a satellite is a satellite and size and shape doesn't matter.

Quote
Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’   

All of these terms are "historical." Planet used to describe "wandering star" because the planets wandered in unpredictable ways across the night sky.

Comet was used to describe a "hairy star"

I accept that there are 8 planets in our solar system, because that seems to be the current consensus.  I could equally accept that the solar system has 13, or 15, or whatever, planets if the definition of ‘planet’ changes.

I accept that Jupiter currently has 79 moons, because that seems to be the consensus, unless the definition of ‘moon’ changes.  I could equally accept that Jupiter has 12 or 20 or whatever moons, if the definition of ‘moon’ changes.  If you insist on including ‘satellite’ as a moon, you should specify it to be a ‘natural satellite’, as NASA does.  Sputnik wasn’t a natural satellite, unlike the Moon.

Everyone ‘knows’ what a planet or a moon is, in the same way that everyone ‘knows’ what a species is.  Except there are at least a dozen definitions of species, the most common one being members of a population capable of interbreeding to produce fertile offspring.  So are polar bears and brown bears members of the same species because they’re capable of interbreeding to produce fertile offspring?  Are unfortunate infertile human couples not members of the same species because they’re unable to produce any offspring, let alone fertile ones?

Planets don’t wander in unpredictable ways across the night sky.  They just move in relation to the far distant stars.  When Herschel first observed Uranus, he thought he’d discovered a new comet.  He observed it over many nights in order to determine its orbit and to be able to predict with great accuracy its position in the night sky.  It wasn’t until he failed to observe a cometary tail that he became convinced he’d discovered a new planet.

Tycho Brahe was able to predict with great accuracy the position of the known planets despite the heliocentric model of the solar system not being the consensus of scientists during his day.  Kepler took his very accurate naked-eye data and used it to derive his three laws of planetary motion.
Title: Episode #688
Post by: CarbShark on September 20, 2018, 10:24:51 PM
Anything not fulfilling these pretty basic and easily applied definitions should have a different name. 

If that would be helpful for astronomers they'd probably do that. But the overwhelming consensus is that a satellite is a satellite and size and shape doesn't matter.

Quote
Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’   

All of these terms are "historical." Planet used to describe "wandering star" because the planets wandered in unpredictable ways across the night sky.

Comet was used to describe a "hairy star"

I accept that there are 8 planets in our solar system, because that seems to be the current consensus.  I could equally accept that the solar system has 13, or 15, or whatever, planets if the definition of ‘planet’ changes.

I accept that Jupiter currently has 79 moons, because that seems to be the consensus, unless the definition of ‘moon’ changes.  I could equally accept that Jupiter has 12 or 20 or whatever moons, if the definition of ‘moon’ changes.  If you insist on including ‘satellite’ as a moon, you should specify it to be a ‘natural satellite’, as NASA does.  Sputnik wasn’t a natural satellite, unlike the Moon.

Everyone ‘knows’ what a planet or a moon is, in the same way that everyone ‘knows’ what a species is.  Except there are at least a dozen definitions of species, the most common one being members of a population capable of interbreeding to produce fertile offspring.  So are polar bears and brown bears members of the same species because they’re capable of interbreeding to produce fertile offspring?  Are unfortunate infertile human couples not members of the same species because they’re unable to produce any offspring, let alone fertile ones?

Planets don’t wander in unpredictable ways across the night sky.  They just move in relation to the far distant stars.  When Herschel first observed Uranus, he thought he’d discovered a new comet.  He observed it over many nights in order to determine its orbit and to be able to predict with great accuracy its position in the night sky.  It wasn’t until he failed to observe a cometary tail that he became convinced he’d discovered a new planet.

Tycho Brahe was able to predict with great accuracy the position of the known planets despite the heliocentric model of the solar system not being the consensus of scientists during his day.  Kepler took his very accurate naked-eye data and used it to derive his three laws of planetary motion.

When the word planet was first used they wandered unpredictably, in that no one could predict their movements, or when or why they would suddenly change direction. 

No, Tycho Brahe was not able to accurately predict the position of the outer planets.


Kepler was the first.





Sent from my iPhone using Tapatalk
Title: Re: Episode #688
Post by: bachfiend on September 20, 2018, 10:55:32 PM
Anything not fulfilling these pretty basic and easily applied definitions should have a different name. 

If that would be helpful for astronomers they'd probably do that. But the overwhelming consensus is that a satellite is a satellite and size and shape doesn't matter.

Quote
Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’   

All of these terms are "historical." Planet used to describe "wandering star" because the planets wandered in unpredictable ways across the night sky.

Comet was used to describe a "hairy star"

I accept that there are 8 planets in our solar system, because that seems to be the current consensus.  I could equally accept that the solar system has 13, or 15, or whatever, planets if the definition of ‘planet’ changes.

I accept that Jupiter currently has 79 moons, because that seems to be the consensus, unless the definition of ‘moon’ changes.  I could equally accept that Jupiter has 12 or 20 or whatever moons, if the definition of ‘moon’ changes.  If you insist on including ‘satellite’ as a moon, you should specify it to be a ‘natural satellite’, as NASA does.  Sputnik wasn’t a natural satellite, unlike the Moon.

Everyone ‘knows’ what a planet or a moon is, in the same way that everyone ‘knows’ what a species is.  Except there are at least a dozen definitions of species, the most common one being members of a population capable of interbreeding to produce fertile offspring.  So are polar bears and brown bears members of the same species because they’re capable of interbreeding to produce fertile offspring?  Are unfortunate infertile human couples not members of the same species because they’re unable to produce any offspring, let alone fertile ones?

Planets don’t wander in unpredictable ways across the night sky.  They just move in relation to the far distant stars.  When Herschel first observed Uranus, he thought he’d discovered a new comet.  He observed it over many nights in order to determine its orbit and to be able to predict with great accuracy its position in the night sky.  It wasn’t until he failed to observe a cometary tail that he became convinced he’d discovered a new planet.

Tycho Brahe was able to predict with great accuracy the position of the known planets despite the heliocentric model of the solar system not being the consensus of scientists during his day.  Kepler took his very accurate naked-eye data and used it to derive his three laws of planetary motion.

When the word planet was first used they wandered unpredictably, in that no one could predict their movements, or when or why they would suddenly change direction. 

No, Tycho Brahe was not able to accurately predict the position of the outer planets.


Kepler was the first.





Sent from my iPhone using Tapatalk

No.  Tycho Brahe was predicting the position of the planets, using his model of the solar system.  Ptolemy was predicting the position of the planets, using his model of the solar system.  Kepler just took Brahe’s accurate data to derive his three laws of planetary motion, including elliptical orbits of planets, which removed the need for epicycles to avoid the predicted position of a planet not matching its actual position.

You’re just wrong again.  Stop digging yourself into a deeper hole.
Title: Re: Episode #688
Post by: The Latinist on September 21, 2018, 12:40:18 AM
Yeah, we’ve been able accurately to predict the movement of the planets, including retrograde motion, for over two thousand years even without an accurate model of the solar system.  I don’t understand why you keep making shit up and then digging in your heels about it.

The planets were so-called not because their motion was unpredictable but because they appear to move against the (apparently) fixed background of the stars.
Title: Re: Episode #688
Post by: CarbShark on September 21, 2018, 02:53:35 AM
Anything not fulfilling these pretty basic and easily applied definitions should have a different name. 

If that would be helpful for astronomers they'd probably do that. But the overwhelming consensus is that a satellite is a satellite and size and shape doesn't matter.

Quote
Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’   

All of these terms are "historical." Planet used to describe "wandering star" because the planets wandered in unpredictable ways across the night sky.

Comet was used to describe a "hairy star"

I accept that there are 8 planets in our solar system, because that seems to be the current consensus.  I could equally accept that the solar system has 13, or 15, or whatever, planets if the definition of ‘planet’ changes.

I accept that Jupiter currently has 79 moons, because that seems to be the consensus, unless the definition of ‘moon’ changes.  I could equally accept that Jupiter has 12 or 20 or whatever moons, if the definition of ‘moon’ changes.  If you insist on including ‘satellite’ as a moon, you should specify it to be a ‘natural satellite’, as NASA does.  Sputnik wasn’t a natural satellite, unlike the Moon.

Everyone ‘knows’ what a planet or a moon is, in the same way that everyone ‘knows’ what a species is.  Except there are at least a dozen definitions of species, the most common one being members of a population capable of interbreeding to produce fertile offspring.  So are polar bears and brown bears members of the same species because they’re capable of interbreeding to produce fertile offspring?  Are unfortunate infertile human couples not members of the same species because they’re unable to produce any offspring, let alone fertile ones?

Planets don’t wander in unpredictable ways across the night sky.  They just move in relation to the far distant stars.  When Herschel first observed Uranus, he thought he’d discovered a new comet.  He observed it over many nights in order to determine its orbit and to be able to predict with great accuracy its position in the night sky.  It wasn’t until he failed to observe a cometary tail that he became convinced he’d discovered a new planet.

Tycho Brahe was able to predict with great accuracy the position of the known planets despite the heliocentric model of the solar system not being the consensus of scientists during his day.  Kepler took his very accurate naked-eye data and used it to derive his three laws of planetary motion.

When the word planet was first used they wandered unpredictably, in that no one could predict their movements, or when or why they would suddenly change direction. 

No, Tycho Brahe was not able to accurately predict the position of the outer planets.


Kepler was the first.





Sent from my iPhone using Tapatalk

No.  Tycho Brahe was predicting the position of the planets, using his model of the solar system.  Ptolemy was predicting the position of the planets, using his model of the solar system.  Kepler just took Brahe’s accurate data to derive his three laws of planetary motion, including elliptical orbits of planets, which removed the need for epicycles to avoid the predicted position of a planet not matching its actual position.

You’re just wrong again.  Stop digging yourself into a deeper hole.
Here we go again. You make unsupported claims say I’m wrong again. But I’m not. Either the  wiki page your skimming has it wrong or your reading comprehension is failing. Or both.

Tycho Brahe did make observations but could not accurately predict the movement of the outer planets. That whole retrograde thing threw everybody. Until Kepler figured it all out.

Title: Re: Episode #688
Post by: bachfiend on September 21, 2018, 03:23:25 AM
Anything not fulfilling these pretty basic and easily applied definitions should have a different name. 

If that would be helpful for astronomers they'd probably do that. But the overwhelming consensus is that a satellite is a satellite and size and shape doesn't matter.

Quote
Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’   

All of these terms are "historical." Planet used to describe "wandering star" because the planets wandered in unpredictable ways across the night sky.

Comet was used to describe a "hairy star"

I accept that there are 8 planets in our solar system, because that seems to be the current consensus.  I could equally accept that the solar system has 13, or 15, or whatever, planets if the definition of ‘planet’ changes.

I accept that Jupiter currently has 79 moons, because that seems to be the consensus, unless the definition of ‘moon’ changes.  I could equally accept that Jupiter has 12 or 20 or whatever moons, if the definition of ‘moon’ changes.  If you insist on including ‘satellite’ as a moon, you should specify it to be a ‘natural satellite’, as NASA does.  Sputnik wasn’t a natural satellite, unlike the Moon.

Everyone ‘knows’ what a planet or a moon is, in the same way that everyone ‘knows’ what a species is.  Except there are at least a dozen definitions of species, the most common one being members of a population capable of interbreeding to produce fertile offspring.  So are polar bears and brown bears members of the same species because they’re capable of interbreeding to produce fertile offspring?  Are unfortunate infertile human couples not members of the same species because they’re unable to produce any offspring, let alone fertile ones?

Planets don’t wander in unpredictable ways across the night sky.  They just move in relation to the far distant stars.  When Herschel first observed Uranus, he thought he’d discovered a new comet.  He observed it over many nights in order to determine its orbit and to be able to predict with great accuracy its position in the night sky.  It wasn’t until he failed to observe a cometary tail that he became convinced he’d discovered a new planet.

Tycho Brahe was able to predict with great accuracy the position of the known planets despite the heliocentric model of the solar system not being the consensus of scientists during his day.  Kepler took his very accurate naked-eye data and used it to derive his three laws of planetary motion.

When the word planet was first used they wandered unpredictably, in that no one could predict their movements, or when or why they would suddenly change direction. 

No, Tycho Brahe was not able to accurately predict the position of the outer planets.


Kepler was the first.





Sent from my iPhone using Tapatalk

No.  Tycho Brahe was predicting the position of the planets, using his model of the solar system.  Ptolemy was predicting the position of the planets, using his model of the solar system.  Kepler just took Brahe’s accurate data to derive his three laws of planetary motion, including elliptical orbits of planets, which removed the need for epicycles to avoid the predicted position of a planet not matching its actual position.

You’re just wrong again.  Stop digging yourself into a deeper hole.
Here we go again. You make unsupported claims say I’m wrong again. But I’m not. Either the  wiki page your skimming has it wrong or your reading comprehension is failing. Or both. Brahe did make observations but could not accurately predict the movement of the outer planets. That whole retrograde thing threw everybody. Until Kepler figured.


Sent from my iPhone using Tapatalk

No, you’re wrong.  And anyway, I wasn’t using Wikipedia to confirm the facts I’m recounting.  Tycho Brahe was predicting the position of the planets in the night sky, as was Ptolemy.  They knew where to look in the night sky at any time to find the planets.  Humans have been predicting the position of planets (and stars) for thousands of years.  Kepler wasn’t able to more accurately predict the position of the planets, but he was able to come up with a better model of the solar system, which did away with the necessary epicycles of Ptolemy’s and Copernicus’s models.

What’s wrong with you?  Do you have a need to disagree with me, either when you’re wrong (as in this case) or when I’m actually not disagreeing with you?  I don’t disagree that the current definition of moons include any body orbiting a planet.  I’m just arguing that the definition should change.  In the same way that I argue that Trump shouldn’t be re-elected in 2020. Not that my wishes have any influence on the re-election of Trump or the definition of moons.
Title: Re: Episode #688
Post by: CarbShark on September 21, 2018, 03:24:44 AM

History of Astronomy (http://abyss.uoregon.edu/~js/ast121/lectures/lec02.html)
Quote
Beyond Tycho Brahe's accomplishments in the observational arena, he is also remembered for introducing two compromise solutions to the solar system model now referred to as the geoheliocentric models. Brahe was strongly influenced by the idea of Mercury and Venus revolving around the Sun to explain the fact that their apparent motion across the sky never takes them more than a few tens of degrees from the Sun (called their greatest elongation). The behavior of inner worlds differs from the orbital behavior of the outer planets, which can be found at any place on the elliptic during their orbital cycle.


Brahe proposed a hybrid solutions to the geocentric model which preserves the geocentric nature of the Earth at the center of the Universe, but placed the inner planets (Mercury and Venus) in orbit around the Sun. This configuration resolves the problem of Mercury and Venus lack of large angular distances from the Sun, but saves the key criticism of the heliocentric model, that the Earth is in motion. In other works, Brahe's geoheliocentric model fit the available data but followed the philosophical intuition of a non-moving Earth.

Neither successfully predicts the motion of the planets. The solution will be discovered by a student of Tycho's, who finally resolves the heliocentric cosmology with the use of elliptical orbits.


Kepler (1600's) a student of Tycho who used Brahe's database to formulate the Laws of Planetary Motion which corrects the problems of epicycles in the heliocentric theory by using ellipses instead of circles for orbits of the planets.

Title: Re: Episode #688
Post by: CarbShark on September 21, 2018, 03:33:37 AM
Anything not fulfilling these pretty basic and easily applied definitions should have a different name. 

If that would be helpful for astronomers they'd probably do that. But the overwhelming consensus is that a satellite is a satellite and size and shape doesn't matter.

Quote
Anything orbiting a star which isn’t large enough to be spherical is an asteroid or a comet (and ‘comet’ is a historical term originating from the cometary tail).  Perhaps anything orbiting a planet not large enough to be spherical could be called a ‘planetary asteroid?’   

All of these terms are "historical." Planet used to describe "wandering star" because the planets wandered in unpredictable ways across the night sky.

Comet was used to describe a "hairy star"

I accept that there are 8 planets in our solar system, because that seems to be the current consensus.  I could equally accept that the solar system has 13, or 15, or whatever, planets if the definition of ‘planet’ changes.

I accept that Jupiter currently has 79 moons, because that seems to be the consensus, unless the definition of ‘moon’ changes.  I could equally accept that Jupiter has 12 or 20 or whatever moons, if the definition of ‘moon’ changes.  If you insist on including ‘satellite’ as a moon, you should specify it to be a ‘natural satellite’, as NASA does.  Sputnik wasn’t a natural satellite, unlike the Moon.

Everyone ‘knows’ what a planet or a moon is, in the same way that everyone ‘knows’ what a species is.  Except there are at least a dozen definitions of species, the most common one being members of a population capable of interbreeding to produce fertile offspring.  So are polar bears and brown bears members of the same species because they’re capable of interbreeding to produce fertile offspring?  Are unfortunate infertile human couples not members of the same species because they’re unable to produce any offspring, let alone fertile ones?

Planets don’t wander in unpredictable ways across the night sky.  They just move in relation to the far distant stars.  When Herschel first observed Uranus, he thought he’d discovered a new comet.  He observed it over many nights in order to determine its orbit and to be able to predict with great accuracy its position in the night sky.  It wasn’t until he failed to observe a cometary tail that he became convinced he’d discovered a new planet.

Tycho Brahe was able to predict with great accuracy the position of the known planets despite the heliocentric model of the solar system not being the consensus of scientists during his day.  Kepler took his very accurate naked-eye data and used it to derive his three laws of planetary motion.

When the word planet was first used they wandered unpredictably, in that no one could predict their movements, or when or why they would suddenly change direction. 

No, Tycho Brahe was not able to accurately predict the position of the outer planets.


Kepler was the first.





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No.  Tycho Brahe was predicting the position of the planets, using his model of the solar system.  Ptolemy was predicting the position of the planets, using his model of the solar system.  Kepler just took Brahe’s accurate data to derive his three laws of planetary motion, including elliptical orbits of planets, which removed the need for epicycles to avoid the predicted position of a planet not matching its actual position.

You’re just wrong again.  Stop digging yourself into a deeper hole.
Here we go again. You make unsupported claims say I’m wrong again. But I’m not. Either the  wiki page your skimming has it wrong or your reading comprehension is failing. Or both. Brahe did make observations but could not accurately predict the movement of the outer planets. That whole retrograde thing threw everybody. Until Kepler figured.


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No, you’re wrong.  And anyway, I wasn’t using Wikipedia to confirm the facts I’m recounting.  Tycho Brahe was predicting the position of the planets in the night sky, as was Ptolemy.  They knew where to look in the night sky at any time to find the planets.  Humans have been predicting the position of planets (and stars) for thousands of years.  Kepler wasn’t able to more accurately predict the position of the planets, but he was able to come up with a better model of the solar system, which did away with the necessary epicycles of Ptolemy’s and Copernicus’s models.

What’s wrong with you?  Do you have a need to disagree with me, either when you’re wrong (as in this case) or when I’m actually not disagreeing with you?  I don’t disagree that the current definition of moons include any body orbiting a planet.  I’m just arguing that the definition should change.  In the same way that I argue that Trump shouldn’t be re-elected in 2020. Not that my wishes have any influence on the re-election of Trump or the definition of moons.

It's not me, pal, you don't know what you're talking about. Again. No humans could accurately predict the position of the outer planets until Kepler. They roughly knew about Mars and Jupiter positions, but had no way to predict when they would go retrograde. The reason Kepler was able to figure it out is he had Tycho's observations, Capernicus heliocentric model and a mastery of math and geometry.



Title: Re: Episode #688
Post by: bachfiend on September 21, 2018, 03:53:05 AM

History of Astronomy (http://abyss.uoregon.edu/~js/ast121/lectures/lec02.html)
Quote
Beyond Tycho Brahe's accomplishments in the observational arena, he is also remembered for introducing two compromise solutions to the solar system model now referred to as the geoheliocentric models. Brahe was strongly influenced by the idea of Mercury and Venus revolving around the Sun to explain the fact that their apparent motion across the sky never takes them more than a few tens of degrees from the Sun (called their greatest elongation). The behavior of inner worlds differs from the orbital behavior of the outer planets, which can be found at any place on the elliptic during their orbital cycle.


Brahe proposed a hybrid solutions to the geocentric model which preserves the geocentric nature of the Earth at the center of the Universe, but placed the inner planets (Mercury and Venus) in orbit around the Sun. This configuration resolves the problem of Mercury and Venus lack of large angular distances from the Sun, but saves the key criticism of the heliocentric model, that the Earth is in motion. In other works, Brahe's geoheliocentric model fit the available data but followed the philosophical intuition of a non-moving Earth.

Neither successfully predicts the motion of the planets. The solution will be discovered by a student of Tycho's, who finally resolves the heliocentric cosmology with the use of elliptical orbits.


Kepler (1600's) a student of Tycho who used Brahe's database to formulate the Laws of Planetary Motion which corrects the problems of epicycles in the heliocentric theory by using ellipses instead of circles for orbits of the planets.


CarbShark,

Do you have problems with reading comprehension?  Your linked article states that Ptolemy’s and Brahe’s models didn’t predict the motion of the planets (they had to include added complex epicycles to the planets’ motions, and Copernicus’ model had even more epicycles than Ptolemy).  But they predicted the position of the planets in the night sky, once the necessary epicycles were added, which made the prediction of the planets’ motion inaccurate.

Kepler’s model was no more accurate in predicting the position of the planets, but it was more accurate in predicting the motion of the planets in doing away with the need to have epicycles.
Title: Re: Episode #688
Post by: Alex Simmons on September 21, 2018, 04:47:23 AM
The problem is Mars is on a low fat diet, Saturn has been keto and Jupiter just eats what it likes. They all claim to be superior in performance and shedding weight, but a long term study has determined none of them has really worked all that much better than the other. Except Jupiter by a little which does swallow more than the others but still loses weight because it's farting a lot.
Title: Re: Episode #688
Post by: bachfiend on September 21, 2018, 06:06:22 AM
Yeah, we’ve been able accurately to predict the movement of the planets, including retrograde motion, for over two thousand years even without an accurate model of the solar system.  I don’t understand why you keep making shit up and then digging in your heels about oit.

The planets were so-called not because their motion was unpredictable but because they appear to move against the (apparently) fixed background of the stars.

I missed your comment.  I apologise for not noticing it, which actually stated the true facts much more concisely that I was able to do.  CarbShark didn’t to object to your correction of CarbShark’s inaccuracies as he did to mine.  Does he show some psychopathology in having an urge to disagree with me even if he’s wrong?
Title: Episode #688
Post by: CarbShark on September 21, 2018, 11:00:33 AM
Yeah, we’ve been able accurately to predict the movement of the planets, including retrograde motion, for over two thousand years even without an accurate model of the solar system.  I don’t understand why you keep making shit up and then digging in your heels about it.

Does the following apply to you as well?

To be constitutionally incapable of admitting when one is wrong, as you have proved yourself over and over again, is incompatible with skepticism, CarbShark. It’s okay: everyone’s wrong sometimes, and this is one of your times.  Just admit that you didn’t know what you were talking about and move on. Perhaps even grow a little humbler because of the experience.

So which is it, have humans been able to accurately predict the movements of the outer planets for thousands of years? or was it Brahe with his models that had Earth at the center? or did it not happen until after Brahe died when his student Kepler, using Brahe's observations, solved the motion of the planets and introduced his first and second, then his third laws of planetary motion that are still valid today?

I've provided citations supporting my position.

No, BF, they do not say what you claim, yes, Brahe had models so did Ptolemy before him. But they didn't work accurately. Brahe thought Mercury and Venus orbited the Sun while the Sun and outer planets orbited Earth. But, surprise, his models weren't accurate predictors or the movement of planets. The Copernican heliocentric model was not widely accepted because it didn't fit the math (they were all using perfect circles (with those loop de loops) and constant speed).

It wasn't until Kepler realized that planets had elliptical orbits and changed speed in orbit that we could make accurate predictions of the positions of all the planets including retrograde motion.

Either post links to good evidence supporting your position, or admit you're both wrong and move on.
Title: Re: Episode #688
Post by: The Latinist on September 21, 2018, 12:00:08 PM
Carbshark, you're conflating motion in space (i.e., epliptical orbits with the sun at one focus) with motion across the sky.  The former (which is what the sources you post are talking about) of course wasn't accurately predicted by a geocentric model with circular orbits and epicycles; but the latter was.  That was what the epicycles were for, and they worked remarkably well to within the tolerances of available measurements.  Brahe's claims to fame are his more accurate instruments which were able to make even more precise measurements that couldn't be explained by existing epicycle models (though they could probably have been extended to account for them) and the religiousness with which he took those measurements from night to night over decades.

I will take issue with one thing that Bachfiend said, though; Keppler's model was, in fact, more accurate than then-existing epicycle models, which didn't fully account for minute changes appearing for the first time in Brahe's data.  But that doesn't mean that epicycle models hadn't been able accurately to predict the motions of the planets as we observed them for two a millennium and a half before that or that they couldn't have continued, with adjustments, to account for the motions of the planets indefinitely.
Title: Re: Episode #688
Post by: CarbShark on September 21, 2018, 01:40:11 PM
Carbshark, you're conflating motion in space (i.e., epliptical orbits with the sun at one focus) with motion across the sky.  The former (which is what the sources you post are talking about) of course wasn't accurately predicted by a geocentric model with circular orbits and epicycles; but the latter was.  That was what the epicycles were for, and they worked remarkably well to within the tolerances of available measurements.  Brahe's claims to fame are his more accurate instruments which were able to make even more precise measurements that couldn't be explained by existing epicycle models (though they could probably have been extended to account for them) and the religiousness with which he took those measurements from night to night over decades.

I will take issue with one thing that Bachfiend said, though; Keppler's model was, in fact, more accurate than then-existing epicycle models, which didn't fully account for minute changes appearing for the first time in Brahe's data.  But that doesn't mean that epicycle models hadn't been able accurately to predict the motions of the planets as we observed them for two a millennium and a half before that or that they couldn't have continued, with adjustments, to account for the motions of the planets indefinitely.

Evidence? I've posted my link, with the parts that directly contradict what you're claiming quoted and bolded, so there's no doubt exactly what the claim is.

The stumbling block until Kepler was accurately predicting when Mars and Jupiter would go retrograde.  And that's exactly their motion across the sky. They could not do that with any accuracy. Not with any days, or even weeks, reliably. Is it any surprise that a model with round orbits and round loop de loops all of a consistent speed didn't match the observations of elliptical orbits of varying speed?

Also, this was less an issue for Science and more of an issue for Astrology. No Prince or General of the time wanted to begin a major undertaking just before Mars went retrograde. That was a bad omen and they believed that shit.

Being the first to accurately and reliably predict retrograde movement was a boon for Astrology. Being able to explain why and the mechanics was a boon for Science.

Kepler was a fucking genius.
Title: Re: Episode #688
Post by: bachfiend on September 21, 2018, 03:41:56 PM
CarbShark,

Carl Sagan in ‘the Demon Haunted World’ recounts of when he first seriously studied science at college and noted that the science faculty took seriously the teaching of the history and philosophy of science, even teaching Ptolemy’s model of the solar system so well that some of the students came to doubt the heliocentric model of the solar system.

The fact remains as has been pointed out to you multiple times, humans have been predicting accurately the position and motion of the planets and the stars in the night sky (that is, as seen from the Earth) for thousands of years regardless of what model of the solar system was accepted; whether the sun and planets (and the sun and the moon were called planets too because they moved in relation to the ‘unchanging’ stars) were pulled by gods in chariots drawn by horses, Ptolemy’s model, Brahe’s model or Copernicus’ model).

We’ve had the benefit of having centuries of acceptance that the the heliocentric model is true.  From a hypothetical fixed point in space outside the solar system, preferably well above the plane of the solar system, Ptolemy’s and Brahe’s models don’t accurately describe (or predict) the position or motion of the planets in space (which aren’t the same as the position and motion of the planets in the night sky, as seen from the Earth).  Copernicus’ model was less inaccurate in describing the position and motion of the planets in space.  Kepler’s model was more accurate, and it became completely accurate when General Relativity was added in 1915 explaining anomalies in Mercury’s orbits, until then unexplained and unpredicted.

Kepler’s brilliance was introducing a paradigm shift - a new view of thinking of reality.  There were very good reasons for thinking that the Earth was stationary and fixed in space.  Humans had accurately been predicting the position and motion of the planets (which included the sun and moon for thousands of years  - including predicting lunar and solar eclipses).  There’s little direct evidence that the Earth is moving.   Foucault’s pendulum, demonstrating the Earth’s rotation, was only suggested in 1851.   Michelson’s and Morley’s Experiment in 1887 provided ‘evidence’ that the Earth is stationary in that the speed of light is constant regardless of the purported motion of the Earth in space - which wasn’t explained until Einstein and Special Relativity in 1905.

Kepler wasn’t the first to accurately the position and motion of the planets in the night sky.  He was just one of many.  And it’s continuing.  We still can’t accurately predict the position and the motion of the planets in space, which seriously impacts on our ability to predict the position and motion of the planets in the night sky.  The Three Body Problem is still unsolved, ‘’solutions’ being obtained by successive iterations of calculations.  Milankovitch cycles are unpredictable more than 60 million years in the future, which seriously impacts on our ability to predict the position of the planets in the night sky.  We can’t predict how rapidly the Moon will continue to recede from the Earth.  Tiny errors in measuring the current position of Neptune results in its predicted position in space varying by the diameter of its orbit.
Title: Re: Episode #688
Post by: CarbShark on September 21, 2018, 04:16:43 PM
CarbShark,

Carl Sagan in ‘the Demon Haunted World’ recounts of when he first seriously studied science at college and noted that the science faculty took seriously the teaching of the history and philosophy of science, even teaching Ptolemy’s model of the solar system so well that some of the students came to doubt the heliocentric model of the solar system.

The fact remains as has been pointed out to you multiple times, humans have been predicting accurately the position and motion of the planets and the stars in the night sky (that is, as seen from the Earth) for thousands of years regardless of what model of the solar system was accepted; whether the sun and planets (and the sun and the moon were called planets too because they moved in relation to the ‘unchanging’ stars) were pulled by gods in chariots drawn by horses, Ptolemy’s model, Brahe’s model or Copernicus’ model).

We’ve had the benefit of having centuries of acceptance that the the heliocentric model is true.  From a hypothetical fixed point in space outside the solar system, preferably well above the plane of the solar system, Ptolemy’s and Brahe’s models don’t accurately describe (or predict) the position or motion of the planets in space (which aren’t the same as the position and motion of the planets in the night sky, as seen from the Earth).  Copernicus’ model was less inaccurate in describing the position and motion of the planets in space.  Kepler’s model was more accurate, and it became completely accurate when General Relativity was added in 1915 explaining anomalies in Mercury’s orbits, until then unexplained and unpredicted.

Kepler’s brilliance was introducing a paradigm shift - a new view of thinking of reality.  There were very good reasons for thinking that the Earth was stationary and fixed in space.  Humans had accurately been predicting the position and motion of the planets (which included the sun and moon for thousands of years  - including predicting lunar and solar eclipses).  There’s little direct evidence that the Earth is moving.   Foucault’s pendulum, demonstrating the Earth’s rotation, was only suggested in 1851.   Michelson’s and Morley’s Experiment in 1887 provided ‘evidence’ that the Earth is stationary in that the speed of light is constant regardless of the purported motion of the Earth in space - which wasn’t explained until Einstein and Special Relativity in 1905.

Kepler wasn’t the first to accurately the position and motion of the planets in the night sky.  He was just one of many.  And it’s continuing.  We still can’t accurately predict the position and the motion of the planets in space, which seriously impacts on our ability to predict the position and motion of the planets in the night sky.  The Three Body Problem is still unsolved, ‘’solutions’ being obtained by successive iterations of calculations.  Milankovitch cycles are unpredictable more than 60 million years in the future, which seriously impacts on our ability to predict the position of the planets in the night sky.  We can’t predict how rapidly the Moon will continue to recede from the Earth.  Tiny errors in measuring the current position of Neptune results in its predicted position in space varying by the diameter of its orbit.

I'm not going to take your word for it or Latinists. (especially since what you just posted disagrees with what both of you posted yesterday).

I've provided evidence that Kepler was indeed the first to accurately predict the motions of all the planets. Before Kepler the retrograde motion of the outer planets could not be accurately predicted. Kepler's laws of the motion of the planets changed astronomy (and astrology) forever. (and the issue of accuracy isn't tiny effects extrapolated millions of years into the future. As I said, before Kepler no one could predict retrograde for the outer planets with a reliable accuracy of days or even weeks.
Title: Re: Episode #688
Post by: The Latinist on September 21, 2018, 05:20:31 PM
If anyone would like to look at some actual data, here (http://inference-review.com/article/ptolemy-versus-copernicus) are some tables giving several years of brahe’s data showing the errors of the Ptolemaic and Copernican systems. Note that the figures for Ptolemy and Copernicus were taken from tables of planetary ephemera calculated years in advance but limited by the accuracy of the observational data available to those who calculated the tables. You can see that both models generally are able to predict both the latitude and longitude to within 1°, usually significantly better.  In general, Copernicus’ model is better for the superior planets because of the way Ptolemy handled the deferents.
Title: Re: Episode #688
Post by: bachfiend on September 21, 2018, 05:34:26 PM
Kepler was the first to come up with an accurate model of the motion of the planets in space, with the elliptical non-circular orbits of the planets.  He didn’t know why this was so.  It wasn’t until Newton with his universal gravitation theory around 60 years later that the mathematical foundations were established.  So actually, the first scientist to accurately predict the position and motion of the planets in space (not just the position and motion of the planets in the night sky as seen from the Earth, which aren’t the same things) came well after Kepler.

Until the mathematical basis of planetary motion was worked out, predicting the motion and position of the planets was little more than numerology.  Even Newton couldn’t work out how the planets maintained stable orbits over very long periods.  He thought God gave the planets a nudge from time to time to keep their orbits stable.

Laplace in 1802 published a monumental 5 volume work on planetary mechanics.  Napoleon read it, and asked why God wasn’t mentioned, and was told by Laplace that he didn’t need that hypothesis.

Kepler was brilliant, no doubt.  I’m particularly impressed by his third law.  But humans were accurately predicting the position and motion of the planets in the night sky before Kepler, provided the necessary epicycles are added.  Copernicus’ model introduced a paradigm shift and explained a lot, including the existence of days and seasons.  But his model with circular orbits required even more epicycles than Ptolemy’s model so it was more complex, despite being equally predictive.  Kepler’s model was no more predictive, it worked with existing data, but it was simpler, and explained everything Copernicus’ model did.
Title: Re: Episode #688
Post by: The Latinist on September 21, 2018, 06:08:14 PM
Bachfiend, I have to disagree with you on your last point: Kepler’s theory was in fact more predictive than Coppernicus’ or Ptolemy’s.  Both Copernicus’ and Ptolemy’s models essentially assumed (if reduced to equivalent mathematics) that the orbits of planets were flattened circles rather than elipses.  They also failed to account for orbital inclination or the fact that planets more at different velocities at different points in their orbits.  This resulted in errors generally of less than 1° but occasionally higher. Kepler was able to eliminate those errors, and his calculations conformed almost precisely to Brahe’s new, more accurate data.

That doesn’t mean that Ptolemy wasn’t able accurately to predict the motion of the stars; he was.  But Kepler was definitely able to do so better.
Title: Re: Episode #688
Post by: Alex Simmons on September 21, 2018, 06:13:13 PM
Mayans were pretty good at predicting things like the return of Venus in the sky. Their system had an error compared with actual of less than 1/1000th of a percent. For Mars they were slightly less accurate at 1/800th of a percent.

The Babylonians had even more accurate predictive ability - similarly their system was not based on "laws" or any cosmological approach, rather they just came up with a complex blend of mathematical formulas to fit the empirical data. That works pretty well and is an approached used to accurately provide predictive capacity in many systems. Fourier transforms come to mind.

It was the Greeks who sought to look at the problem from a cosmological standpoint and come up with some rationale to describe the observed motions.

Use of a geocentric approach with circles and epicycles has its issues but that can still be a very accurate method of prediction if you layer sufficient number of well chosen functions together (and the primary one is subtraction of the Earth-Sun orbit function from the planetary orbit function). Indeed if you describe laws in a non-inertial frame of reference then one could just as well come up with a set of laws of motion that will predict with high precision, all you need is to make up a bunch of imaginary forces that match the observations. They'll just be bloody hard to calculate. But it can certainly be done with high precision and accuracy.

Progression to heliocentric model and Kepler's laws of planetary motion was a great leap forward because it greatly simplified the predictive process, but to the say earlier processes were not accurate or could not be accurate is not really true. It comes down to processing power (which of course is limited and slow when done manually) and how many suitable functions or imaginary forces could be layered to explain the observed reality.

It reminds me of the goldfish view analogy Stephen Hawking describes in his book The Grand Design. Excerpt:
http://publicism.info/science/grand/3.html

Just because a view is distorted by using a different frame of reference doesn't mean one cannot construct models with high degree of predictive ability.
Title: Re: Episode #688
Post by: CarbShark on September 21, 2018, 06:38:53 PM
Mayans were pretty good at predicting things like the return of Venus in the sky. Their system had an error compared with actual of less than 1/1000th of a percent. For Mars they were slightly less accurate at 1/800th of a percent.

Are you saying they were able to accurately predict when Mars would go retrograde?

1/800th of a percent of what?

Quote
The Babylonians had even more accurate predictive ability - similarly their system was not based on "laws" or any cosmological approach, rather they just came up with a complex blend of mathematical formulas to fit the empirical data. That works pretty well and is an approached used to accurately provide predictive capacity in many systems. Fourier transforms come to mind.

Are you saying they were able to accurately predict when Mars would go retrograde?

Quote
It was the Greeks who sought to look at the problem from a cosmological standpoint and come up with some rationale to describe the observed motions.

Use of a geocentric approach with circles and epicycles has its issues but that can still be a very accurate method of prediction if you layer sufficient number of well chosen functions together (and the primary one is subtraction of the Earth-Sun orbit function from the planetary orbit function). Indeed if you describe laws in a non-inertial frame of reference then one could just as well come up with a set of laws of motion that will predict with high precision, all you need is to make up a bunch of imaginary forces that match the observations. They'll just be bloody hard to calculate. But it can certainly be done with high precision and accuracy.

Are you saying they were able to accurately predict when Mars would go retrograde?

Quote

Progression to heliocentric model and Kepler's laws of planetary motion was a great leap forward because it greatly simplified the predictive process, but to the say earlier processes were not accurate or could not be accurate is not really true. It comes down to processing power (which of course is limited and slow when done manually) and how many suitable functions or imaginary forces could be layered to explain the observed reality.
But they didn't and they couldn't.

Here's the thing. They knew how many days it takes Mars to orbit the Sun. They even knew how many hours. That was unchangeable and easily predictable.

What they did not know, until Kepler was when Mars would go retrograde.

And that was important to them (because of Astrology).

If you're claiming they (anyone before Kepler) had that ability, I'll need to evidence.


 
Title: Re: Episode #688
Post by: Alex Simmons on September 21, 2018, 07:13:29 PM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.
Title: Re: Episode #688
Post by: The Latinist on September 21, 2018, 07:18:14 PM
An Analysis of Ptolmey’s treatment of Retrograde Motion (http://adsbit.harvard.edu//full/1998JHA....29..257M/0000257.000.html)

JHA xxix (1989) p.257ff
Title: Re: Episode #688
Post by: bachfiend on September 21, 2018, 08:21:29 PM
CarbShark,

If you’d written that Kepler was first to have come up with an accurate model of the solar system, with its elliptical orbits of the planets, no one would have disagreed with you. 

The interesting questions are the questions Kepler didn’t ask.  Why are the planetary orbits elliptical?  No idea - it was an ad hoc explanation to match the observations of the data.  Why can’t the elliptical planetary orbits become perfect circular orbits over time with a natural urge to perfection? (Well, actually they do to a certain extent.  One of the Milankovitch cycles involves the Earth’s orbit becoming more or less circular over the course of the cycle).  Why does the solar system consist of 4 rocky inner planets, an asteroid belt, 4 outer gas giants, a Kuiper belt with a plethora of bodies of varying size including the planet (!) Pluto (there, I’ve nailed my colours to the mast - I think Pluto should be called a planet, not a dwarf planet) and an Oort cloud?  Why doesn’t the solar system have Jupiter close to the sun as a ‘hot Jupiter’ which is common in other planetary systems, with the inner rocky planets kicked out of the solar system? (It’s been suggested that it’s the existence of Saturn that managed to prevent the inner migration of Jupiter).

Humans were accurately predicting the position of the planets before Kepler.  Ptolemy just added more epicycles to get agreement with the observed data.  Kepler wasn’t the first to do so, and he certainly wasn’t the last.  He wouldn’t have been able to know anything about how the night sky would have looked from the Earth just 11000 years in the future, knowing nothing about Milankovitch cycles (for all I know, Kepler might not have thought that a problem, with the Earth just 6000 years old and the Second Coming nigh - Kepler lived in very ‘interesting’ times with the Reformation and the Counter Reformation and the impending Thirty Years War which devastated Central Europe.
Title: Re: Episode #688
Post by: CarbShark on September 21, 2018, 09:07:09 PM

If you’d written that Kepler was first to have come up with an accurate model of the solar system, with its elliptical orbits of the planets, no one would have disagreed with you. 

I wouldn't agree with that. I'd say Kepler came up with the most accurate model of the solar system to that date, with the elliptical orbits of planets, the variable speeds of orbits.

And  he was the first to accurately and reliably predict the motion of the planets. Previous models were not accurate nor reliable for the apparent retrograde motion of the outer planets, especially Mars.

The interesting questions are the questions Kepler didn’t ask.  Why are the planetary orbits elliptical? 
I'm sure he did ask, the answer was "I dunno" (in German, of course)

Why can’t the elliptical planetary orbits become perfect circular orbits over time with a natural urge to perfection?
   

That's actually not a question for science.

(Well, actually they do to a certain extent.)
One of the Milankovitch cycles involves the Earth’s orbit becoming more or less circular over the course of the cycle). 

If that's the case it doesn't support your claim.


Why does the solar system consist of 4 rocky inner planets, an asteroid belt, 4 outer gas giants, a Kuiper belt with a plethora of bodies of varying size including the planet (!) Pluto (there, I’ve nailed my colours to the mast - I think Pluto should be called a planet, not a dwarf planet) and an Oort cloud?

OK, this is now silly.

 I can tell you why he didn't ask those questions.

Kepler did not know the difference between rocky planets and gas giants.

Kepler never saw the planet Pluto (we apparently have found something to agree on); nor Uranus nor Neptune. They weren't discovered until long after he died.

Why doesn’t the solar system have Jupiter close to the sun as a ‘hot Jupiter’ which is common in other planetary systems, with the inner rocky planets kicked out of the solar system? (It’s been suggested that it’s the existence of Saturn that managed to prevent the inner migration of Jupiter).

Why didn't Kepler, in the 17th century, ask why our solar system's planets didn't follow the distribution pattern of exoplanets discovered in the 21st century?

I can guess why.

Humans were accurately predicting the position of the planets before Kepler. 

Not consistently and accurately.

Ptolemy just added more epicycles to get agreement with the observed data. 

Did not consistently and accurately predict retrograde motion of the outer planets.


Kepler wasn’t the first to do so, and he certainly wasn’t the last. 

He was the first,  to accurately and reliably predict the apparent retrograde motion of Mars, Jupiter and Saturn.

Anyone who has done it since has used Kepler's laws of the motions of planets to do so.
Title: Re: Episode #688
Post by: CarbShark on September 22, 2018, 05:13:20 PM

The Project Gutenberg eBook of Great Astronomers, by Sir Robert S. Ball. (http://www.gutenberg.org/files/2298/2298-h/2298-h.htm#PTOLEMY)


Quote
Before Tycho was seventeen he had commenced the difficult task of calculating the movements of the planets and the places which they occupied on the sky from time to time. He was not a little surprised to find that the actual positions of the planets differed very widely from those which were assigned to them by calculations from the best existing works of astronomers. With the insight of genius he saw that the only true method of investigating the movements of the heavenly bodies would be to carry on a protracted series of measurements of their places. This, which now seems to us so obvious, was then entirely new doctrine. Tycho at once commenced regular observations in such fashion as he could.

Quote
Kepler was also the first astronomer who ever ventured to predict the occurrence of that remarkable phenomenon, the transit of a planet in front of the sun's disc. He published, in 1629, a notice to the curious in things celestial, in which he announced that both of the planets, Mercury and Venus, were to make a transit across the sun on specified days in the winter of 1631. The transit of Mercury was duly observed by Gassendi, and the transit of Venus also took place, though, as we now know, the circumstances were such that it was not possible for the phenomenon to be witnessed by any European astronomer.

In addition to Kepler's discoveries already mentioned, with which his name will be for ever associated, his claim on the gratitude of astronomers chiefly depends on the publication of his famous Rudolphine tables. In this remarkable work means are provided for finding the places of the planets with far greater accuracy than had previously been attainable.

Quote
Kepler, it must be always remembered, was not an astronomical observer. It was his function to deal with the observations made by Tycho, and, from close study and comparison of the results, to work out the movements of the heavenly bodies. It was, in fact, Tycho who provided as it were the raw material, while it was the genius of Kepler which wrought that material into a beautiful and serviceable form. For more than a century the Rudolphine tables were regarded as a standard astronomical work.
Title: Re: Episode #688
Post by: CarbShark on September 22, 2018, 05:22:48 PM
An Analysis of Ptolmey’s treatment of Retrograde Motion (http://adsbit.harvard.edu//full/1998JHA....29..257M/0000257.000.html)

JHA xxix (1989) p.257ff

I'm curious, what are you suggesting this shows?

Title: Re: Episode #688
Post by: CarbShark on September 22, 2018, 06:53:43 PM
If anyone would like to look at some actual data, here (http://inference-review.com/article/ptolemy-versus-copernicus) are some tables giving several years of brahe’s data showing the errors of the Ptolemaic and Copernican systems. Note that the figures for Ptolemy and Copernicus were taken from tables of planetary ephemera calculated years in advance but limited by the accuracy of the observational data available to those who calculated the tables. You can see that both models generally are able to predict both the latitude and longitude to within 1°, usually significantly better.  In general, Copernicus’ model is better for the superior planets because of the way Ptolemy handled the deferents.

Quotes from your own source:
Quote
Because Copernicus relied on the Aristotelian requirement that the planets move in circles, his theory was not capable of predicting planetary positions with perfect accuracy. Only with Johannes Kepler’s discovery of elliptical planetary orbits could the heliocentric system consistently predict planetary motion.

Quote
The analysis offered here has demonstrated that Tycho compared the predictions of planetary positions made by Copernicus and Ptolemy with his own observations and indeed found, on balance, Copernicus to be superior.

So your source concludes Copernicus' predictions were better than Ptolemy's. And Kepler's are better than both of them.

It was Kepler's model that first accurately and reliably predicted the movement of planets. No Ptolemy, not Copernicus, not no one else, not no how.

As to your dismissing the errors as 1° and often less, that's the equivalent of two moons. (The moon is half a degree or 30'). And yes a good number of Tycho's observations found that level of precision. But, a good number also found much larger differences.

While we got somewhat better measurements between Ptolemy and Brahe. Not enough to account for a difference of the width of one moon. Neither used telescopes and both were able to pinpoint their positions relative to other stars. And even then, even if it were the case the Ptolemy's model was off because of the inferiority of his observations, that supports my argument, that his model was not able to accurately and reliably predict the positions of the planets. An excuse for an error, does not erase the error. Maybe you're right maybe that's why his model was not accurate, but the point is that the model was not accurate.

I would suggest that when Ptolemy and Copernicus both have errors of 2 to 4° in the position of Mars they are missing retrograde motion. (4° would be the width of 8 moons)

A difference of 4° is hardly accurate, and to have that occur frequently, even if many other observations are closer to 1 moon's width, does not suggest reliability.

Using that data you'd be sending European princes off to war, without know when Mars would go retrograde. That's about as useless as an Astrologer could possibly be.
Title: Re: Episode #688
Post by: Quetzalcoatl on September 23, 2018, 04:41:51 PM
I think they should re-invite Neil deGrasse Tyson to discuss the optimal definition of planet. I know that he has opinions on the issue.
Title: Re: Episode #688
Post by: Tassie Dave on September 23, 2018, 04:52:53 PM
I think they should re-invite Neil deGrasse Tyson to discuss the optimal definition of planet. I know that he has opinions on the issue.

or Phil Plait, or Pamela Gay.

All 3 would have a more informed opinion.
Title: Re: Episode #688
Post by: Quetzalcoatl on September 23, 2018, 05:14:40 PM
I think they should re-invite Neil deGrasse Tyson to discuss the optimal definition of planet. I know that he has opinions on the issue.

or Phil Plait, or Pamela Gay.

All 3 would have a more informed opinion.

Good point.

I'm not saying Steve is uninformed, he is obviously very smart and well-read. But astronomy is not his area of expertize, and astronomers (and those with related expertize) such as those mentioned might have counter-points to his idea that they would then articulate and discuss the subject.

Or maybe they would actually agree with Steve's proposal? I don't know.
Title: Re: Episode #688
Post by: CarbShark on September 23, 2018, 05:17:18 PM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.

That absolutely does not mean they could predict retrograde motion. That's not enough information. You would also need to know about the elliptical shape of the orbit and the variable speed of both bodies and they did not know that.

 And, once again you offering very specific information, but no citation.

Where are these numbers coming from? Your Astrologer?



Title: Re: Episode #688
Post by: The Latinist on September 23, 2018, 05:21:44 PM
NDT is the Pluto-killer and has very strong opinions on the subject. If you wanted both extremes, get both NDT and a One of the planetologists who believes that large moons should also be called planets.  Another good choice would be Michael E. Brown, who’s discovered many of the largest TNO’s and who seems to think they should not be called planets.
Title: Re: Episode #688
Post by: CarbShark on September 23, 2018, 05:25:14 PM
I think they should re-invite Neil deGrasse Tyson to discuss the optimal definition of planet. I know that he has opinions on the issue.

or Phil Plait, or Pamela Gay.

All 3 would have a more informed opinion.

Good point.

I'm not saying Steve is uninformed, he is obviously very smart and well-read. But astronomy is not his area of expertize, and astronomers (and those with related expertize) such as those mentioned might have counter-points to his idea that they would then articulate and discuss the subject.

Or maybe they would actually agree with Steve's proposal? I don't know.

That's an interesting question, and would make for a good conversation, but the bigger question is do they agree with the IAU position, that IAU should set the definition of planet, etc., or Metzger's position that the taxonomy of astronomy should be done through the scientific method, developing a consensus via published work and conferences. 

That's far more important for science than the merits of one set of criteria over another.
Title: Re: Episode #688
Post by: brilligtove on September 23, 2018, 06:12:26 PM
I agree about finding concensus through papers and conferences - but I thought the IAU made the decision at a conference of astronomers?
Title: Re: Episode #688
Post by: CarbShark on September 23, 2018, 07:48:06 PM
Yes. They took a vote. Since when does science vote? 


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Title: Re: Episode #688
Post by: Alex Simmons on September 23, 2018, 07:52:53 PM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.

That absolutely does not mean they could predict retrograde motion. That's not enough information. You would also need to know about the elliptical shape of the orbit and the variable speed of both bodies and they did not know that.

 And, once again you offering very specific information, but no citation.

Where are these numbers coming from? Your Astrologer?

Please try not to be an arsehole. Is there something wrong with attempting to have civil discourse?

I agree it's not enough information to be super precise but it is enough information to calculate estimates of when retrograde motion will occur, or more broadly, the Greek Letter Phenomena (http://www.caeno.org/pdf/F009_Greek%20Letter%20Phenomena.pdf).

Such estimates require certain assumptions, including that orbits are circular. The Earth's orbit is quite circular (as are most of the naked eye plants except Mercury), Mars much less so, hence the limit in precision one can predict such retrograde motion for Mars compared with the other planets. This is what was found when Babylonian methods were examined.

I agree that with Kepler's laws and greater detail on the eccentricity of the orbits such predictions can be made far more accurately.

As for the Babylonians specifically, there has been plenty of published information analysing the accuracy of their predictions for "Greek Letter Phenomena", which includes prediction of the stationary points in the apparent motion of the naked-eye planets.

Mars is, not unexpectedly, the one with the least precision in such predictions made by the Babylonians. Still they had models that were very good and their predictions for the motion of planets were remarkably accurate.

Reference Chapter 4 (The effectiveness of the Goal-Year type planetary periods) of this paper which discusses the accuracy of the Babylonian predictions for the Greek Letter Phenomena:

GRAY, JENNIFER,MARY,KNIGHTLEY (2009) A Study of Babylonian Goal-Year Planetary Astronomy,
Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/101/

Looking at the tables in section 4.4 we see that using their 79 year period for Mars they could prediction the Greek Letter Phenomena (including stationary points) to within 3 days 97% of the time, and using a 284 year period their accuracy improved to predicting GLP to within 3 days 99% of the time. Predictions to within 1 day they were not so reliable, attaining that 87% of the time.

Excerpt (p. 87) with table showing predictive accuracy for Mars and Jupiter:

(https://i.imgur.com/1ppW2oo.png)

With their methods, their prediction of Mars' apparent motion is the least accurate of the naked eye planets.

Their predictions for timing of the Greek Letter Phenomena for the other planets to within 3 days is 100%, and to within 1 day also 100% of the time for all but Mercury which could be predicted within 1 day 99% of the time.

That's damned impressive.

They use both data collected over centuries as a means of prediction (via Goal Year texts), as well as devised mathematical models to attempt to fit their observations.
Title: Re: Episode #688
Post by: CarbShark on September 23, 2018, 08:40:32 PM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.

That absolutely does not mean they could predict retrograde motion. That's not enough information. You would also need to know about the elliptical shape of the orbit and the variable speed of both bodies and they did not know that.

 And, once again you offering very specific information, but no citation.

Where are these numbers coming from? Your Astrologer?

Please try not to be an arsehole. Is there something wrong with attempting to have civil discourse?

Wow. I don't think I've been uncivil whatsoever.


From your own source:

Quote
Table 4.3c summarises the theoretical date corrections for Mars‘ Greek-letter phenomena. It shows that Mars‘ phenomena do not recur as precisely as Mercury‘s or Venus‘. Clearly most of the shorter attested periods for Mars are somewhat imprecise: compared with Mercury and Venus, where the most common date correction would be within a few days of all of the records, for Mars there is a wider range of date differences.

These are not reporting on the positions of the planets, merely the dates they apparent retrograde motion begins and ends, etc.

Three days is not accurate or precise. Neither is one day, compared to Kepler's predictions which include exact position and date and time of retrograde motion.

I'm not saying they're not impressive. They are simply not accurate, reliable or precise.

Title: Re: Episode #688
Post by: Alex Simmons on September 24, 2018, 12:06:01 AM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.

That absolutely does not mean they could predict retrograde motion. That's not enough information. You would also need to know about the elliptical shape of the orbit and the variable speed of both bodies and they did not know that.

 And, once again you offering very specific information, but no citation.

Where are these numbers coming from? Your Astrologer?

Please try not to be an arsehole. Is there something wrong with attempting to have civil discourse?

Wow. I don't think I've been uncivil whatsoever.


From your own source:

Quote
Table 4.3c summarises the theoretical date corrections for Mars‘ Greek-letter phenomena. It shows that Mars‘ phenomena do not recur as precisely as Mercury‘s or Venus‘. Clearly most of the shorter attested periods for Mars are somewhat imprecise: compared with Mercury and Venus, where the most common date correction would be within a few days of all of the records, for Mars there is a wider range of date differences.

These are not reporting on the positions of the planets, merely the dates they apparent retrograde motion begins and ends, etc.

Three days is not accurate or precise. Neither is one day, compared to Kepler's predictions which include exact position and date and time of retrograde motion.

I'm not saying they're not impressive. They are simply not accurate, reliable or precise.
Perhaps your style comes across differently to what you think it does.

You specifically asked about predictions of when a planet goes retrograde. I provided published evidence of the Babylonian's capacity to do that to within a precision of 1 day. Which is the same level of accuracy I quoted much earlier in this thread that you suggested was not backed up by evidence. As to predicting other positions, when you are already predicting the timing of Greek Letter Phenomena, then interpolating a position on a given day would not be overly difficult for people with the capability displayed by the Babylonians.

Your statement that the Babylonian predictions are neither precise nor accurate is completely subjective.
It was at the level that I had quoted earlier, a level you disputed.

That subsequent analysis and models by Kepler and others were able to improve on the precision and accuracy is neither here nor there.
Title: Re: Episode #688
Post by: CarbShark on September 24, 2018, 12:42:08 AM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.

That absolutely does not mean they could predict retrograde motion. That's not enough information. You would also need to know about the elliptical shape of the orbit and the variable speed of both bodies and they did not know that.

 And, once again you offering very specific information, but no citation.

Where are these numbers coming from? Your Astrologer?

Please try not to be an arsehole. Is there something wrong with attempting to have civil discourse?

Wow. I don't think I've been uncivil whatsoever.


From your own source:

Quote
Table 4.3c summarises the theoretical date corrections for Mars‘ Greek-letter phenomena. It shows that Mars‘ phenomena do not recur as precisely as Mercury‘s or Venus‘. Clearly most of the shorter attested periods for Mars are somewhat imprecise: compared with Mercury and Venus, where the most common date correction would be within a few days of all of the records, for Mars there is a wider range of date differences.

These are not reporting on the positions of the planets, merely the dates they apparent retrograde motion begins and ends, etc.

Three days is not accurate or precise. Neither is one day, compared to Kepler's predictions which include exact position and date and time of retrograde motion.

I'm not saying they're not impressive. They are simply not accurate, reliable or precise.

You specifically asked about predictions of when a planet goes retrograde. I provided published evidence of the Babylonian's capacity to do that to within a precision of 1 day.

Some of there predictions were that precise. But others were not.
Quote
Which is the same level of accuracy I quoted much earlier in this thread that you suggested was not backed up by evidence.


You were throwing out numbers earlier with no source or context. And no they don’t correlate with what your source says.

Quote
As to predicting other positions, when you are already predicting the timing of Greek Letter Phenomena, then interpolating a position on a given day would not be overly difficult for people with the capability displayed by the Babylonians.

That is not relevant. Kepler made a great kep forward in developing a model that consistently, accurately and reliably predicted the motions of all the planets.

His timing errors were measured in seconds not days and his position errors were measured in degree seconds, not minutes or degrees.


Quote
Your statement that the Babylonian predictions are neither precise nor accurate is completely subjective.
It was at the level that I had quoted earlier, a level you disputed.

Kepler’s errors at least an order magnitude more accurate that the errors of any that came before him.
Quote

That subsequent analysis and models by Kepler and others were able to improve on the precision and accuracy is neither here nor there.

That’s exactly the point. This entire rat hole is that you, Latinist and BF for some reason dispute that Kepler was the first to accurately, reliably and consistently predict the motion of the Planets. Not just the six he knew of but all those we’ve found since.





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Title: Re: Episode #688
Post by: Alex Simmons on September 24, 2018, 12:49:57 AM
I quoted an accuracy level that the detailed paper I referred to provides evidentiary support. To less than one hundredth of a percent.

That you don't consider that accurate or precise is your subjective assessment.
Title: Re: Episode #688
Post by: CarbShark on September 24, 2018, 01:12:29 AM
I quoted an accuracy level that the detailed paper I referred to provides evidentiary support. To less than one hundredth of a percent.

That you don't consider that accurate or precise is your subjective assessment.

They only reach that level of accuracy in their best case. You're ignoring their errors, which ignores their inconsistency and unreliability.

Astronomy does not consider errors of that magnitude to be accurate or precise.

To dismiss that as subjective is bogus. Using that logic, just getting the accuracy within a week would be fine. It's as if you're moving the goalposts backward.

Title: Re: Episode #688
Post by: Alex Simmons on September 24, 2018, 05:55:16 PM
I quoted an accuracy level that the detailed paper I referred to provides evidentiary support. To less than one hundredth of a percent.

That you don't consider that accurate or precise is your subjective assessment.

They only reach that level of accuracy in their best case. You're ignoring their errors, which ignores their inconsistency and unreliability.

Astronomy does not consider errors of that magnitude to be accurate or precise.

To dismiss that as subjective is bogus. Using that logic, just getting the accuracy within a week would be fine. It's as if you're moving the goalposts backward.

I really don't get the big fat strawman you keep building.

I am not talking about accuracy levels of astronomy today and I'm not moving any goalposts. I simply stated the level of accuracy they attained and provided evidence for that because you disputed it. Predicting a planetary position with a day or so over hundreds of years. That this is not considered accurate in today's sophisticated astronomical world is neither here nor there.
Title: Re: Episode #688
Post by: CarbShark on September 24, 2018, 06:58:57 PM
I quoted an accuracy level that the detailed paper I referred to provides evidentiary support. To less than one hundredth of a percent.

That you don't consider that accurate or precise is your subjective assessment.

They only reach that level of accuracy in their best case. You're ignoring their errors, which ignores their inconsistency and unreliability.

Astronomy does not consider errors of that magnitude to be accurate or precise.

To dismiss that as subjective is bogus. Using that logic, just getting the accuracy within a week would be fine. It's as if you're moving the goalposts backward.

I really don't get the big fat strawman you keep building.

I am not talking about accuracy levels of astronomy today and I'm not moving any goalposts. I simply stated the level of accuracy they attained and provided evidence for that because you disputed it. Predicting a planetary position with a day or so over hundreds of years. That this is not considered accurate in today's sophisticated astronomical world is neither here nor there.

And what I'm saying is that is misleading. You are only referring to the best case scenarios ad ignoring the misses.

And, while that may or may not matter to you the claim that is being disputed is that Kepler was the first to accurately, precisely and reliably calculate the positions of the planets.

Based on the data provided so far the advantage is by an order of magnitude.

 
Title: Re: Episode #688
Post by: bachfiend on September 24, 2018, 08:19:42 PM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.

That absolutely does not mean they could predict retrograde motion. That's not enough information. You would also need to know about the elliptical shape of the orbit and the variable speed of both bodies and they did not know that.

 And, once again you offering very specific information, but no citation.

Where are these numbers coming from? Your Astrologer?

The elliptical shape of the orbit and the variable speed of both (Mars and the Earth) aren’t the cause of the retrograde movement of Mars.

The retrograde movement of Mars in the night sky as seen from the Earth is due to the Earth, being on the inner faster orbit to Mars, overtaking Mars.  Before the Earth overtakes Mars, Mars appears to be in constellations ahead of Mars.  After the Earth has overtaken Mars, Mars appears in constellations behind Mars.  And then the Earth ‘turns’ the corner to pass behind the Sun and is going in the opposite direction to Mars, and the movement of Mars in the night sky as seen from the Earth appears to reverse yet again.

The time when this is going to happen is entirely predictable, regardless of whether one is using the Ptolemy, Brahe, Copernicus or Kepler model of the solar system.  It occurs when Mars is in opposition to the Earth, when Mars is on the opposite side of the Earth to the Sun, when it’s closest, brightest and highest in the night sky.  This is predictable, regardless of which model is used.  Ptolemy knew where to find Mars in the night sky.

The difference between the models is that Ptolemy’s and Brahe’s models used epicycles to explain retrograde motion of the outer planets.  Mars is orbiting in a perfect circle a point which is orbiting the Earth in a perfect circle, but at a faster speed, and when Mars is highest and brightest in the night sky as seen from the Earth, it’s moving on its epicycle in the opposite direction to its orbit around the Sun.

The length of the epicycle has to be exact, so it’s an ad hoc explanation (Copernicus’ and Kepler’s explanation of retrograde motion are much more natural, not relying on the length of the orbital period of Mars to be such an exact multiple of the length of its epicycle), but it’s doable.  Ptolemy’s model described the motion of the planets in the night sky as seen from the Earth perfectly well, and was accepted as true for hundreds of years.  Some planetaria have working Ptolemy models with reliable depictions of the positions of the other planets in the night sky.

Kepler’s model most accurately describes the motions of the planets in space, with its elliptical planetary orbits.  But the retrograde motion of the outer planets is something different.  Regardless of the model used, all can be used to predict the motion of the planets in the night sky.
Title: Re: Episode #688
Post by: brilligtove on September 24, 2018, 08:53:29 PM
It occurs when Mars is in opposition to the Earth, when Mars is on the opposite side of the Earth to the Sun, when it’s closest, brightest and highest in the night sky.

I think you mistyped. Opposition is when the planets are closest on the same side of the sun. (I had to look that up stupid legacy name.) :)

http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/retromars.html
Title: Re: Episode #688
Post by: Alex Simmons on September 24, 2018, 09:04:34 PM
I quoted an accuracy level that the detailed paper I referred to provides evidentiary support. To less than one hundredth of a percent.

That you don't consider that accurate or precise is your subjective assessment.

They only reach that level of accuracy in their best case. You're ignoring their errors, which ignores their inconsistency and unreliability.

Astronomy does not consider errors of that magnitude to be accurate or precise.

To dismiss that as subjective is bogus. Using that logic, just getting the accuracy within a week would be fine. It's as if you're moving the goalposts backward.

I really don't get the big fat strawman you keep building.

I am not talking about accuracy levels of astronomy today and I'm not moving any goalposts. I simply stated the level of accuracy they attained and provided evidence for that because you disputed it. Predicting a planetary position with a day or so over hundreds of years. That this is not considered accurate in today's sophisticated astronomical world is neither here nor there.

And what I'm saying is that is misleading. You are only referring to the best case scenarios ad ignoring the misses.

And, while that may or may not matter to you the claim that is being disputed is that Kepler was the first to accurately, precisely and reliably calculate the positions of the planets.

Based on the data provided so far the advantage is by an order of magnitude.
I take it you didn't read the paper. In it they discuss the various model options identified by the Babylonians and the ones the Babylonians settled on as best fitting the observed data, along with evidence of their careful and methodical application of calendar corrections. It took centuries but they got there.

You are now on my ignore list. Congratulations, you're the only one.
Title: Re: Episode #688
Post by: Alex Simmons on September 24, 2018, 09:09:30 PM
It occurs when Mars is in opposition to the Earth, when Mars is on the opposite side of the Earth to the Sun, when it’s closest, brightest and highest in the night sky.

I think you mistyped. Opposition is when the planets are closest on the same side of the sun. (I had to look that up stupid legacy name.) :)

http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/retromars.html
What Bachfiend wrote is correct, as is what you wrote. They mean the same thing.

Just re-read what s/he wrote:
when Mars is on the opposite side of the Earth to the Sun
Title: Re: Episode #688
Post by: bachfiend on September 24, 2018, 09:14:14 PM
It occurs when Mars is in opposition to the Earth, when Mars is on the opposite side of the Earth to the Sun, when it’s closest, brightest and highest in the night sky.

I think you mistyped. Opposition is when the planets are closest on the same side of the sun. (I had to look that up stupid legacy name.) :)

http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/retromars.html

I don’t think I mistyped.  I meant that the Sun, the Earth and Mars are on a line, with the Sun at one end of the line, and Mars on the opposite end of the line, with the Earth in the middle, so that Mars is closest, brightest and highest in the night sky.

We recently enjoyed this.  When I was taking my dog for our walk in the dark frigidly cold Perth winter predawn mornings, I enjoyed admiring how bright and disc-like Mars appeared to be in the western sky before it set.

I can’t say that I noticed retrograde motion of Mars though.
Title: Re: Episode #688
Post by: brilligtove on September 24, 2018, 10:44:05 PM
Ah... You didn't mis-type. I misunderstood. I was thinking you meant 'opposite side of the sun from the earth' and was confustigated.
Title: Re: Episode #688
Post by: CarbShark on September 24, 2018, 11:15:04 PM
The Babylonians had a good measure of both the sidereal and synodic period of Mars, which means they could predict when it would go retrograde. Their accuracy level for this was about 4 days in 284 years or ~0.004%.

That absolutely does not mean they could predict retrograde motion. That's not enough information. You would also need to know about the elliptical shape of the orbit and the variable speed of both bodies and they did not know that.

 And, once again you offering very specific information, but no citation.

Where are these numbers coming from? Your Astrologer?

The elliptical shape of the orbit and the variable speed of both (Mars and the Earth) aren’t the cause of the retrograde movement of Mars.


No one said they were. They are, however, the confounders that make it impossible to predict the apparent retrograde motion of Mars (and other planets) with the accuracy, precision and reliability that the Kepler model has.
Quote
The retrograde movement of Mars in the night sky as seen from the Earth is due to the Earth, being on the inner faster orbit to Mars, overtaking Mars.  Before the Earth overtakes Mars, Mars appears to be in constellations ahead of Mars.  After the Earth has overtaken Mars, Mars appears in constellations behind Mars.  And then the Earth ‘turns’ the corner to pass behind the Sun and is going in the opposite direction to Mars, and the movement of Mars in the night sky as seen from the Earth appears to reverse yet again.

That's a pretty convoluted explanation.

Quote

The time when this is going to happen is entirely predictable, regardless of whether one is using the Ptolemy, Brahe, Copernicus or Kepler model of the solar system.  It occurs when Mars is in opposition to the Earth, when Mars is on the opposite side of the Earth to the Sun, when it’s closest, brightest and highest in the night sky.  This is predictable, regardless of which model is used.  Ptolemy knew where to find Mars in the night sky.

This is one of the things you're getting wrong. It's precisely because both planets have elliptical orbits and variable speeds that epicycles can't achieve anything  like the precision that Kepler does.

In the case of Ptolemy when his data was off it was off by as much as 5 degrees, that's about the width of 10 moons.

So to say he knew where to find mars in the night sky, doesn't narrow it down that much. Yea, Mars is in the night sky somewhere.  That's not accurate, precise and he couldn't reliably do any better.
Quote


The difference between the models is that Ptolemy’s and Brahe’s models used epicycles to explain retrograde motion of the outer planets.  Mars is orbiting in a perfect circle a point which is orbiting the Earth in a perfect circle, but at a faster speed, and when Mars is highest and brightest in the night sky as seen from the Earth, it’s moving on its epicycle in the opposite direction to its orbit around the Sun.
Perfect circles vs. elliptical orbits; constant speeds vs. variable speeds; no synchronization between orbits (in other words one year opposition could occur with one planet near apogee and the other near perigree; the next opposition could be the opposite or any random internal between for either. Same for conjunction, of course.
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The length of the epicycle has to be exact, so it’s an ad hoc explanation (Copernicus’ and Kepler’s explanation of retrograde motion are much more natural, not relying on the length of the orbital period of Mars to be such an exact multiple of the length of its epicycle), but it’s doable. 

Here is where I think you are wrong. Without resorting to ellipses and variable speeds I don't believe that any system of epicycles, no matter how exact, could reliably and consistently  achieve the precision that Kepler did.

The Mayans couldn't; the Babylonians couldn't; Ptolemy couldn't; Capernicous couldn't; Brahe couldn't, no one could until Kepler, and anyone who has done it since has used Kepler's laws maybe with minute refinements.


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Ptolemy’s model described the motion of the planets in the night sky as seen from the Earth perfectly well, and was accepted as true for hundreds of years.  Some planetaria have working Ptolemy models with reliable depictions of the positions of the other planets in the night sky.

Perfectly well? This is flat out false. Ptolemy regularly missed retrograde and transits. Again, sometimes by the width of 10 moons.
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Kepler’s model most accurately describes the motions of the planets in space, with its elliptical planetary orbits.  But the retrograde motion of the outer planets is something different.  Regardless of the model used, all can be used to predict the motion of the planets in the night sky.

Flat out false, on both cases. The motions of the planets in space is the cause of the apparent retrograde motion of the outer planets, and understanding the laws that govern the motion of the planets is the best way to understand (and predict) the phenomemon of apparent retrograde motion.
Title: Re: Episode #688
Post by: CarbShark on September 24, 2018, 11:18:58 PM
I can’t say that I noticed retrograde motion of Mars though.

If you used star guides based on Kepler's model you could have known exactly when it was happening.

Not with any models before him.
Title: Re: Episode #688
Post by: bachfiend on September 25, 2018, 12:03:51 AM
I can’t say that I noticed retrograde motion of Mars though.

If you used star guides based on Kepler's model you could have known exactly when it was happening.

Not with any models before him.

There’s no contradiction between Kepler being the first to propose an accurate model of the motion of planets through SPACE, and there being accurate models of the motion of planets through the NIGHT SKY as seen from the Earth.

We’ve had the advantage of thinking in terms of heliocentrism for centuries.  Trying to think how pre-Kleperians saw the solar system is difficult.  You’re making the same mistake.  Yes, we know that planetary orbits are elliptical.  And that epicycles don’t work regularly with elliptical orbits, so wouldn’t be an explanation of retrograde motion of the outer planets at opposition.  But the orbits of the planets were assumed to be perfect circles.  As were the epicycles, which makes it very regular, albeit very contrived.

Kepler almost certainly wasn’t able to predict the position of the planets in space far into the future, let alone in the night sky.  Newton, who most people would agree was much savvier than Kepler, and who developed the mathematical basis of the gravitational motion of planets, couldn’t understand how the orbits of the planets could be stable, thinking that God gave the planets a nudge from time to time, to keep the planets in position.  And this was around 60 years after Kepler.  It wasn’t until the 19th century, and Laplace’s monumental 5-volume on planetary mechanics, that it was begun to be understood.

I didn’t notice the retrograde motion of Mars because I was too busy enjoying the view of Mars.  And I wasn’t walking the dog at the same time each morning.  I wasn’t identifying stars near Mars in the line of sight and trying to determine whether they were apparently closer or further away, which a professional astronomer such as Ptolemy would be doing.
Title: Re: Episode #688
Post by: CarbShark on September 25, 2018, 10:23:55 AM
I can’t say that I noticed retrograde motion of Mars though.

If you used star guides based on Kepler's model you could have known exactly when it was happening.

Not with any models before him.

There’s no contradiction between Kepler being the first to propose an accurate model of the motion of planets through SPACE, and there being accurate models of the motion of planets through the NIGHT SKY as seen from the Earth.

I suppose that theoretically it could be possible to come up with a system that would accurately and reliably indicate the position of all the planets in the night sky even if you don't know how they move through space (in ellipses with variable speeds).

But, no one did. The problem for Ptolemy, Caperinicus (and Brahe) was that they were using perfect circles and constant speeds and epicycles with perfect circles and constant speeds.

I believe that it's probably impossible to build a model that accurately, consistently and reliably indicates the position of planets in the night sky using perfect circles and constant speeds, epicycles.

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We’ve had the advantage of thinking in terms of heliocentrism for centuries.  Trying to think how pre-Kleperians saw the solar system is difficult.  You’re making the same mistake. 

What mistake? Pre-Capernicus the belief (in the west) was everything revolved around the earth. That's not difficult to imagine. After Capernicus  it was undecided precisely because they were unable to accurately predict the positions of the planets in the night sky. Their thinking was that if the model were correct it should be exact. And they were right.

The problem was  they were using perfect circles and constant speeds. The epicycles were introduced to attempt to correct those errors. But just didn't work.

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Kepler almost certainly wasn’t able to predict the position of the planets in space far into the future, let alone in the night sky. 

False on both. It is because he was able to accurately and reliably predict the position of the planets in the night sky that science adopted the heliocentric model of the solar system.

And, yes his model works far into the future.

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Newton, who most people would agree was much savvier than Kepler, and who developed the mathematical basis of the gravitational motion of planets, couldn’t understand how the orbits of the planets could be stable, thinking that God gave the planets a nudge from time to time, to keep the planets in position.  And this was around 60 years after Kepler.  It wasn’t until the 19th century, and Laplace’s monumental 5-volume on planetary mechanics, that it was begun to be understood.

I don't know what you're saying about Newton but is sounds like nonsense. Kepler and Capernicus were among the giants upon whose shoulders Newton stood on.

I don't think you know what you're talking about with Laplace. His contribution to planetary mechanics was to explain the minor perturbations in the orbits of planets due to the influence of the gravity of other planets. No small feat, but to claim that's when planetary mechanics was begun to be understood is also nonsense.

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I didn’t notice the retrograde motion of Mars because I was too busy enjoying the view of Mars.  And I wasn’t walking the dog at the same time each morning.  I wasn’t identifying stars near Mars in the line of sight and trying to determine whether they were apparently closer or further away, which a professional astronomer such as Ptolemy would be doing.

How did you know it was Mars?
Title: Re: Episode #688
Post by: bachfiend on September 25, 2018, 02:36:07 PM
CarbShark,

I knew Mars was Mars because it was obvious.  It was very bright, very red, and very obvious.  It was shining with an intense constant light and looked completely different to the surrounding stars, and looked as though it was a very tiny but definite disc, unlike the stars, which were definite points.  Mars was easy to pick out, just like Jupiter in its recent opposition (and when Jupiter was in opposition, I was also able to identify the 4 inner moons with a good pair of binoculars - confirmed with an astronomy App later).

Astronomers, even amateurs, don’t have any difficulty in picking out planets.  As the names state, they move.  Pre-Keplerian astronomers were observing the night sky for thousands of years, trying to understand the heavens.  They went to extraordinary lengths to preserve the illusion that the Earth is stationary and that everything in the heavens is perfect, orbiting the Earth in perfect circles.  And added the ad hoc explanation of epicycles, and epicycles on epicycles, to explain and predict obvious phenomena to them such as the retrograde movement of the outer planets.

Ptolemy’s model of the solar system can be constructed in planetaria using clock-work type mechanical models, and they work reliably.  Kepler’s model of the solar system has the very real advantage that it’s much simpler and not contrived as Ptolemy’s, Brahe’s or Copernicus’ models.  And the very great advantage that it also turned out to be true.  Kepler had also devised an earlier model of the solar system based on perfect shapes, which was absolute nonsense.

True explanations have the very real advantage that in retrospect they appear obvious, even at the time they were proposed, and previous explanations, even ones which were well accepted, appear ludicrous - in retrospect.

The earlier models of the solar system were based on the illusion that the universe is an entirely predictable clockwork-like creation, whereas now we realise that it’s a chaotic system with small initial perturbations producing later large differences, so it’s essentially unpredictable far into the future.  Milankovitch cycles, which are unpredictable beyond 60 million years, make predictions of the motions of the planets through the night sky unpredictable using simple models such as Kepler’s even just thousands of years in the future.
Title: Re: Episode #688
Post by: CarbShark on September 25, 2018, 03:05:59 PM

I knew Mars was Mars because it was obvious.  It was very bright, very red, and very obvious.  It was shining with an intense constant light and looked completely different to the surrounding stars, and looked as though it was a very tiny but definite disc, unlike the stars, which were definite points.  Mars was easy to pick out, just like Jupiter in its recent opposition (and when Jupiter was in opposition, I was also able to identify the 4 inner moons with a good pair of binoculars - confirmed with an astronomy App later).
I've noticed that in this conversation you make more claims than anyone else, and provide less evidence (zero, actually) to support your claims.

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Astronomers, even amateurs, don’t have any difficulty in picking out planets.  As the names state, they move. 

This is incorrect. The motion of planets is virtually undetectable by the human eye. And the further visible planets (Saturn especially) moves so slowly it can appear to be stationary over a period of days.

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Pre-Keplerian astronomers were observing the night sky for thousands of years, trying to understand the heavens.  They went to extraordinary lengths to preserve the illusion that the Earth is stationary and that everything in the heavens is perfect, orbiting the Earth in perfect circles.  And added the ad hoc explanation of epicycles, and epicycles on epicycles, to explain and predict obvious phenomena to them such as the retrograde movement of the outer planets.

And you know what, had they been accurate in predicting the precise locations of the planets; when solar transits would occur; when Mars and Jupiter would begin and end apparent retrograde motion; then that model of the solar system would have lasted much longer. Maybe centuries. There would not have been a push to find an accurate model if the one they had seemed accurate.

Copernicus may not have proposed the heliocentric model if they had reliable predictors; Kepler would have been content with the current model, had it worked; without Kepler's laws of planetary motion Newton may not have understood universal gravity; etc. etc.

It's because they could not explain or predict those phenomena that they kept looking for ways to explain them.

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Ptolemy’s model of the solar system can be constructed in planetaria using clock-work type mechanical models, and they work reliably.

Evidence? I dispute this. Yes the model can be replicated in a planetarium. And it does work, showing the dots where the model says they should be, but they don't work in making accurate predictions of things like apparent retrograde motion or even opposition or conjunction with any reliabilty.


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Kepler’s model of the solar system has the very real advantage that it’s much simpler and not contrived as Ptolemy’s, Brahe’s or Copernicus’ models.  And the very great advantage that it also turned out to be true.  Kepler had also devised an earlier model of the solar system based on perfect shapes, which was absolute nonsense.
Plus the advantage of being an accurate description of the solar system and being able to predict all those things with errors an order of magnitude (at least) better than all those others.

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True explanations have the very real advantage that in retrospect they appear obvious, even at the time they were proposed, and previous explanations, even ones which were well accepted, appear ludicrous - in retrospect.

The earlier models of the solar system were based on the illusion that the universe is an entirely predictable clockwork-like creation, whereas now we realise that it’s a chaotic system with small initial perturbations producing later large differences, so it’s essentially unpredictable far into the future.  Milankovitch cycles, which are unpredictable beyond 60 million years, make predictions of the motions of the planets through the night sky unpredictable using simple models such as Kepler’s even just thousands of years in the future.


I don't think not being able to to pinpoint the time and location of Mars a thousand years in advance really bothered medieval princes who didn't want to launch an invasion just before Mars went retrograde.

And while predictions made based purely on Kepler's laws of planetary motion may not have held up over the centuries without refinements, all of those refinements incorporate Kepler's laws.
Title: Re: Episode #688
Post by: The Latinist on September 25, 2018, 03:34:22 PM
I think that ultimately this comes down to an argument about what "accurate."  None of us believes that Ptolmey's or Copernicus' predictions were perfect; we just disagree over whether the imperfections in Ptolmey's numbers amount to it reasonably being said that the planets "wandered unpredictably, in that no one could predict their movements, or when or why they would suddenly change direction."  I do not think that is an accurate statement; people generally (though not always) could predict years in advance to well within a degree where in the sky a planet would be, and they could predict the start and end of retrograde motion to within a few days. I do not think that can accurately be described as "wandering unpredictably."  And it is clear that on that point we will simply have to disagree.

Bachfiend, I want to point out that you are repeating a misimpression of how Ptolmey's model worked (in particular when you say that he used 'epicycles on epicycles.'  The fact is that Ptolemy's model used only one epicycle for each planet along with a displacement of the observer from the earth called the deferrent.  Neither he nor later authors kept adding additional epicycles to account for other motion.  Copernicus was able to eliminate the deferrent by causing the earth to orbit the sun (indeed, the function of the defferent in Ptolmey's model is to compensate for the motion of the earth around the sun -- though Ptolmey didn't know it).
Title: Re: Episode #688
Post by: CarbShark on September 25, 2018, 04:13:33 PM
I think that ultimately this comes down to an argument about what "accurate."  None of us believes that Ptolmey's or Copernicus' predictions were perfect; we just disagree over whether the imperfections in Ptolmey's numbers amount to it reasonably being said that the planets "wandered unpredictably, in that no one could predict their movements, or when or why they would suddenly change direction."  I do not think that is an accurate statement; people generally (though not always) could predict years in advance to well within a degree where in the sky a planet would be, and they could predict the start and end of retrograde motion to within a few days. I do not think that can accurately be described as "wandering unpredictably."  And it is clear that on that point we will simply have to disagree.

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wandered unpredictably, in that no one could predict their movements or when or why they would suddenly change direction."

This is a perfectly reasonable and accurate description of pre-Kepler astronomy. Planets would be moving along nicely in their orbits, then seem to stop, reverse direction, seem to stop, and reverse direction again. This behavior could not be predicted with any reliability or useful precision.

Stopping changing directions is wandering. No one could predict when or why is unpredictable.


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people generally (though not always) could predict years in advance to well within a degree where in the sky a planet would be, and they could predict the start and end of retrograde motion to within a few days. I do not think that can accurately be described as "wandering unpredictably." 

Which of these statements would you disagree with:

Previous models often missed the location of Mars by 5 degrees,  this means they were not consistent or reliable.

They could be off by as much as a month on retrograde motion if they tried to predict years in advance.

(If they tried to predict from a point of it's orbit were it came out of opposition, for example, they could get closer in time but still not that close).
 
The errors that they would regularly generate were an order of magnitude (at least) greater than the errors from Kepler's model.

Kepler's model had the advantage of actually being a good representation of the planets and explained the unexplained behavior.
Title: Re: Episode #688
Post by: CarbShark on September 25, 2018, 04:27:05 PM
https://www.youtube.com/watch?v=EpSy0Lkm3zM
Title: Re: Episode #688
Post by: bachfiend on September 25, 2018, 05:09:17 PM
CarbShark,

I was right when I identified the very bright, very red, very obvious ‘star’ in the western sky in the pre-dawn darkness as Mars, so I’m not making any evidence-free unsupported claims.  Even the local newspapers had noted the fact of the opposition of Mars, and advised their readers to get up early and look at it.

The retrograde motion of Mars and the other outer planets is predictable.  It occurs when the planets are in opposition to the Earth, and that’s entirely predictable for pre-Keplerarian astronomers.

Any evidence that princes decided to go to war based on the position or motions of Mars?  William the Conquerer is said to have decided to invade England based on the appearance of Comet Halley, but Mars?  Why would the position of Mars in future years have any influence on the decision of princes to go to war now instead of later?  The Thirty Years War was started by the 2nd defenestration of Prague in 1618 (Kepler’s domicile), not by Kepler’s more accurate model of the solar system.

This argument is a right royal pain in the arse.  I’m wasting far too much time arguing with you.  I’m dropping out.
Title: Re: Episode #688
Post by: CarbShark on September 25, 2018, 05:23:20 PM

I was right when I identified the very bright, very red, very obvious ‘star’ in the western sky in the pre-dawn darkness as Mars, so I’m not making any evidence-free unsupported claims.  Even the local newspapers had noted the fact of the opposition of Mars, and advised their readers to get up early and look at it.

Still not convinced. I've been at star parties where experienced astronomers got Mars wrong. What constellation were you looking at? Antares is often mistake for Mars by amateurs


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The retrograde motion of Mars and the other outer planets is predictable.  It occurs when the planets are in opposition to the Earth, and that’s entirely predictable for pre-Keplerarian astronomers.

Where the hell is your evidence for that? It is not predictable reliably or accurately. Latinists data was showing predictions were off by the width of 10 moons. That's the equivalent of saying "It's somewhere in that part of the sky". 


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Any evidence that princes decided to go to war based on the position or motions of Mars?  William the Conquerer is said to have decided to invade England based on the appearance of Comet Halley, but Mars?  Why would the position of Mars in future years have any influence on the decision of princes to go to war now instead of later?  The Thirty Years War was started by the 2nd defenestration of Prague in 1618 (Kepler’s domicile), not by Kepler’s more accurate model of the solar system.

No, because they didn't know when it would go retrograde. But all these guys believed in Astrology. Copernicus, Brahe, Kepler they were all astrologers. There really wasn't much of difference between Astronomy and Astrology in those days
Title: Re: Episode #688
Post by: gebobs on September 25, 2018, 05:53:26 PM
Might it be that the bar for accuracy has changed. Sure, the Ptolemaic model was reasonably accurate for the 2nd century CE. After all, what did they need it for other than astrology and predicting eclipses. As such, being off by a few days or a week even wouldn't matter.
Title: Re: Episode #688
Post by: CarbShark on September 25, 2018, 06:08:06 PM
Might it be that the bar for accuracy has changed. Sure, the Ptolemaic model was reasonably accurate for the 2nd century CE. After all, what did they need it for other than astrology and predicting eclipses. As such, being off by a few days or a week even wouldn't matter.

Well, it mattered for a couple reasons. Good and bad. First, Astrology mattered to them and they seriously believed that their lives would be impacted by what was happening in the sky. From day to day.

Retrograde motion of the planets really spooked them because it was unpredictable.

The good is that because it mattered they kept looking for a model of the solar system (to them the entire universe) that worked.

A model that would allow them to precisely predict when and where retrograde motions and transits across the sun and just the position of any planet on any specific date and time.

If that nonsense wasn't important to them then these very very smart people (Ptolemy, Copernicus, Brahe, Kepler, not to mention the Babylonians and Aztecs) wouldn't have dedicated so much of their lives and energy on finding a better way to that.

It's why I'm astounded that Kepler's achievement and his contribution to the advancement of Astronomy is being discounted and minimized here.

But I agree in the grand scheme of things it shouldn't have mattered to them if Mars went retrograde Tuesday or next Thursday. Or if Mercury and Venus both transited the Sun, or if Jupiter went retrograde the day after the crops were planted or the day before.

Luckily for Science and especially Physics and Astronomy Astrology was very important to them in those days.
Title: Re: Episode #688
Post by: Alex Simmons on September 25, 2018, 06:48:07 PM
This argument is a right royal pain in the arse.  I’m wasting far too much time arguing with you.  I’m dropping out.
The mute / block function is neat. I hadn't tried it before. My day is already off to a better start.
Title: Re: Episode #688
Post by: The Latinist on September 25, 2018, 06:52:57 PM
https://www.youtube.com/watch?v=EpSy0Lkm3zM

I stumbled kn that video today, too, but it is not an accurate representation of the Ptolemaic model.

Aside from that, the primary statement about this topic with which I agree is “I’m not going to engage in this discussion any more.”
Title: Re: Episode #688
Post by: CarbShark on September 25, 2018, 08:09:42 PM

Does the following apply to you as well?

To be constitutionally incapable of admitting when one is wrong, as you have proved yourself over and over again, is incompatible with skepticism, CarbShark. It’s okay: everyone’s wrong sometimes, and this is one of your times.  Just admit that you didn’t know what you were talking about and move on. Perhaps even grow a little humbler because of the experience.

At least I know the answer to this question
Title: Re: Episode #688
Post by: God Bomb on October 06, 2018, 08:14:31 AM
Guys I'm confused, why would a lyre bird mimic other birds for mating purposes?  Does it enjoy interspecies relationships?
Title: Re: Episode #688
Post by: arthwollipot on October 21, 2018, 08:20:45 PM
Guys I'm confused, why would a lyre bird mimic other birds for mating purposes?  Does it enjoy interspecies relationships?

Perhaps the female lyrebird sexually selects males based on their ability to mimic the sounds that are found in their environment. It's unlikely that the birds themselves want to mate with cameras and chainsaws.
Title: Re: Episode #688
Post by: God Bomb on October 29, 2018, 02:27:51 PM
Guys I'm confused, why would a lyre bird mimic other birds for mating purposes?  Does it enjoy interspecies relationships?

Perhaps the female lyrebird sexually selects males based on their ability to mimic the sounds that are found in their environment. It's unlikely that the birds themselves want to mate with cameras and chainsaws.

He didn't say they mimic any sound for mating, specifically he said other birds.  Seems like that would just cause massive confusion.
Title: Re: Episode #688
Post by: arthwollipot on October 29, 2018, 07:14:22 PM
Guys I'm confused, why would a lyre bird mimic other birds for mating purposes?  Does it enjoy interspecies relationships?

Perhaps the female lyrebird sexually selects males based on their ability to mimic the sounds that are found in their environment. It's unlikely that the birds themselves want to mate with cameras and chainsaws.

He didn't say they mimic any sound for mating, specifically he said other birds.  Seems like that would just cause massive confusion.

Mimic one sound, mimic other sounds. It may be that the ability to mimic other species of bird is accidental.
Title: Re: Episode #688
Post by: CarbShark on November 08, 2018, 02:45:45 PM
(https://apod.nasa.gov/apod/image/1811/Ma2018La_tezelN1024.jpg)



Astronomy Picture of the Day (https://apod.nasa.gov/apod/)

(https://apod.nasa.gov/apod/image/1811/Ma2018La_tezelN1024.jpg)



Retrograde motion of Mars in 2018 on Vimeo (https://vimeo.com/298439756)
Title: Re: Episode #688
Post by: bachfiend on November 08, 2018, 04:26:51 PM
(https://apod.nasa.gov/apod/image/1811/Ma2018La_tezelN1024.jpg)



Astronomy Picture of the Day (https://apod.nasa.gov/apod/)

(https://apod.nasa.gov/apod/image/1811/Ma2018La_tezelN1024.jpg)



Retrograde motion of Mars in 2018 on Vimeo (https://vimeo.com/298439756)

And your point?

I know what I saw when Mars was in opposition to the Sun this year.  When I was taking my dog for a walk in the pre-dawn darkness, I’d look to the east and see the sky beginning to lighten with the coming sunrise, and then I’d look to the west at 180 degrees to where the Sun was and see a very bright red Mars which was obviously different to the surrounding stars in being a very tiny disc instead of a dot.  And even after sunrise, it was still visible (it’s actually possible sometimes to even see Venus after sunrise if you know where to look for it).

You’re very arrogant in asserting that I was confusing a planet with a star.  Planets are often very obvious.  Jupiter when it’s in opposition to the Earth is often very obvious even when it’s in the vicinity of the full Moon (which is a clue that it’s a planet instead of a star - it’s lying in much the same plane).

The retrograde motion of the outer planets is entirely predictable.  It occurs when they’re in opposition to the Earth.
Title: Re: Episode #688
Post by: CarbShark on November 08, 2018, 04:42:14 PM
WTF?  I just posted some cool images related to what was discussed in this thread. I didn't mention you, wasn't thinking about you, had pretty much forgotten you meaningless little story about seeing mars (or thinking you saw mars).  Get over yourself.
Title: Re: Episode #688
Post by: bachfiend on November 08, 2018, 07:23:57 PM
WTF?  I just posted some cool images related to what was discussed in this thread. I didn't mention you, wasn't thinking about you, had pretty much forgotten you meaningless little story about seeing mars (or thinking you saw mars).  Get over yourself.

I did see Mars.  But what’s your point posting your ‘some cool images?’  The retrograde motion of the outer planets is a well understood and illustrated phenomenon.  You didn’t need to show it again.

As an aside, I saw the film ‘Journey’s End’ yesterday.  It was set on the Western Front near St Quentin from 18-21 March, 1918 on the eve of the German Spring Offensive.  I was bemused it showed the Moon to be almost full (it was actually in the first quarter phase).  Film makers ought to get the little details right.  The Australian television series ‘Gallipoli’ showed the Moon to be a waxing crescent moon on the evening of April 25, 1915 (and had it upside down to boot - it was filmed in South Australia).  It was actually almost a full moon (setting at around 2:30 am around Gallipoli) which determined the tactics and timing of the Allied invasion of Turkey.
Title: Re: Episode #688
Post by: Billzbub on November 09, 2018, 11:00:43 AM
WTF?  I just posted some cool images related to what was discussed in this thread. I didn't mention you, wasn't thinking about you, had pretty much forgotten you meaningless little story about seeing mars (or thinking you saw mars).  Get over yourself.

Thanks CarbShark.  Those were cool pics.