Talk:Definition of planet/definition of planet archive 7
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[edit] Removed paragraph
I have removed the material in italics from the "Double planets" section
"Nonetheless they could be considered as such since, though the Moon orbits the Earth, the timing of its orbit is in tandem with the Earth's own orbit around the Sun — looking down on the ecliptic, the Moon never actually loops back on itself, and in essence it orbits the Sun in its own right. This is true of any moon sufficiently far enough away from its parent body that its orbital speed round the planet is slower than the planet's speed round the Sun. The required distance from the planet to the moon depends on the mass of the planet, and the distance from the planet to the Sun, but not the mass of the moon. If the distance from the Sun to the planet increases, or the planet's mass decreases, then the required distance between the planet and moon increases. Consequently, the same argument could be used that Jupiter and Callisto or Saturn and Iapetus form double planets. "
This may be true, but it has never been sourced, and I can't verify it. If someone can, I'd be happy to see it put back. Serendipodous 22:44, 8 November 2006 (UTC)
- (I added the preceding paragraph to this section to clarify what is being refered to). Serendipodous just gave me a heads up that it had been removed. The reason I never gave a source was that I felt it was self-evident. Is the problem with the following notion...
- If a moon's orbital speed (around its planet) is less than its planet's orbital speed (around the Sun), then looking "down" the moon never actually loops back on itself, and in essence it orbits the Sun in its own right.
- ... or is it the specific examples given? Tompw (talk) (review) 22:07, 26 May 2007 (UTC)
[edit] Definitions of planets in fiction
what about adding a pra. about the Definition of planet in fiction (tv,books etc.) like Star Trek planet classifications 89.1.30.64 03:18, 3 February 2007 (UTC)
- This article is about the scientific definition of a planet, so it would be inappropriate to add fictional information. However, you may be interested in reading Stars and planetary systems in fiction. Cheers. --Ckatzchatspy 03:56, 3 February 2007 (UTC)
[edit] Minor inaccuracy removed
Following the sentence describing Eris as a "Dwarf Planet," I removed this dubious claim: "...although the Minor Planet Center has given it a full minor planet designation: 136199 Eris." This suggests that the designation "Minor planet" is more specific than "dwarf planet" In fact, all 136199+ known small bodies are designated "minor planets." --MiguelMunoz 10:49, 12 February 2007 (UTC)
- Indeed, Pluto has also recently been assigned a minor planet designation - 134340. --Neo 12:11, 12 February 2007 (UTC)
[edit] Future of the Definition?
Does anyone know if the IAU is planning to revisit or revise the new definition of the planet? I have heard of multiple petitions from both the scientific community and public that urge them to do so. --Sly 18:12, 15 March 2007 (UTC)
- Tough call. Alan Stern and Mark Sykes have circulated a petition, and the definition of planet will have to be a topic at the next IAU congress in 2009, if only to deal with the extrasolar issue. However, realistically, I don't think there's any going back. Pluto was placed in the Minor Planet Catalogue, and by the time it comes up for reconsideration in 2009, 42,000 new objects will be ahead of it in the list. Since minor planets are named in chronological order, that would mean that, were Pluto removed from the catalogue, every single one of the 42,000 new objects will need to have its number changed, and not only that, but every single paper that mentioned any of those 42,000 objects would need to be altered as well. My feeling is that, eventually, "Dwarf planet" will be considered a subclass of "planet" and so Pluto will get at least some of its planetary dignity back. However it will still remain a dwarf planet. Perhaps they can add a new designation in the catalogue to list the dwarf planets as special among the minor planets. Serendipodous 19:00, 15 March 2007 (UTC)
- Not to be difficult, but if the decision were made to redesignate, I doubt that something as minor as the numbering would stand in the way. There's no reason to renumber the following objects, no more than there is to retrieve and renumber your cheques if you have to cancel one. Worst case scenario, they could declare 134340 permanently empty ("retired"?) and move on. (Don't forget that Pluto - having been assigned a number 76 years after its discovery - isn't in chronological order anyways.) --Ckatzchatspy 08:56, 16 March 2007 (UTC)
- Again, people forget that this is not only about Pluto. If for some reason Pluto gets back its planethood, it would mean that at least some of the other dwarf planets would also become planets. I don't think that returning to pre-2006 situation is possible. Eight or dozens of planets, but not nine.--JyriL talk 21:54, 17 March 2007 (UTC)
- what the true problem is is that people are getting stuck over a definition. what you call it does not change what it is. i MY opinion, everything that directly orbits the sun and has enough mass to be round is a planet. the true root of the problem is that then there would be like 16 planets, and having a lot of planets is supposed to be bad. i dont understand why anyone thinks this way.
- There wouldn't be 16 planets; there be more like 1600. We just haven't found them all yet. Try getting kids to memorise all those in school. Serendipodous 04:30, 21 March 2007 (UTC)
- i doubt there would be that many, but i get your point. however, i dont see why we have to not call them planets. i dont think it would be that hard to memorize them all. i can remember the 50 states. a planet is pretty much a big thing that orbits a star. if there happens to be a lot of them, so be it.
- This is a common misconception. It's not the number of planets that some astronomers consider a problem; it's their orbits - highly eccentric, or highly inclined, or both; and with huge semi-major axes that are sometimes hard to understand in their own right. Having an object is one thing; explaining how it got there is quite another. Compared to the nearly circular orbits of everything large inside Neptune, that tells you something different has been going on. So it's partially a dynamical and formation issue as well. Spiral Wave 19:49, 28 March 2007 (UTC)
- That may be so of some astronomers, but the definition itself, as decided, is all about number. The distinction between a planet and a dwarf planet is the ratio of its own mass to the mass within its orbital zone. Serendipodous 09:46, 29 March 2007 (UTC)
- I agree. i think that, to the astronomers, it is all about number. i think the true thing that makes this definition strange is that, suddenly, because of where it is, or the shape of its orbit, it is suddenly something else. i think we should exclude what it is DOING and focus on what it IS. i think we should take the planet as if it were alone in a void. nothing else around it. no orbits, no other planets, nothing. then, apply some test (like a size or roundness test) and see if it was a planet. if it passes, its a planet, no matter where it is or how many there are. (i.e. if a strawberry grew out of my nose, you would still call it a strawberry, and if there were suddenly 1000 George Bushes, they wouldnt suddenly not be George Bush) —The preceding unsigned comment was added by 69.177.203.87 (talk) 18:39, 29 March 2007 (UTC).
- True, but then satellites like the Moon and Titan would have to be given similar consideration. I think that would be a perfectly adequate definition of planet, though again perhaps a little difficult for the kiddies to memorise in school.Serendipodous 18:43, 29 March 2007 (UTC)
- Well, we just call them all planets and classify them. you have terrestrial planets, ice planets (pluto like things), gas giants, and moons. —The preceding unsigned comment was added by 64.252.194.190 (talk) 19:04, 30 March 2007 (UTC).
- Not all moons, TNOs or terrestrial objects are planets though. Serendipodous 19:28, 30 March 2007 (UTC)
- Well, we just call them all planets and classify them. you have terrestrial planets, ice planets (pluto like things), gas giants, and moons. —The preceding unsigned comment was added by 64.252.194.190 (talk) 19:04, 30 March 2007 (UTC).
- True, but then satellites like the Moon and Titan would have to be given similar consideration. I think that would be a perfectly adequate definition of planet, though again perhaps a little difficult for the kiddies to memorise in school.Serendipodous 18:43, 29 March 2007 (UTC)
- I agree. i think that, to the astronomers, it is all about number. i think the true thing that makes this definition strange is that, suddenly, because of where it is, or the shape of its orbit, it is suddenly something else. i think we should exclude what it is DOING and focus on what it IS. i think we should take the planet as if it were alone in a void. nothing else around it. no orbits, no other planets, nothing. then, apply some test (like a size or roundness test) and see if it was a planet. if it passes, its a planet, no matter where it is or how many there are. (i.e. if a strawberry grew out of my nose, you would still call it a strawberry, and if there were suddenly 1000 George Bushes, they wouldnt suddenly not be George Bush) —The preceding unsigned comment was added by 69.177.203.87 (talk) 18:39, 29 March 2007 (UTC).
- That may be so of some astronomers, but the definition itself, as decided, is all about number. The distinction between a planet and a dwarf planet is the ratio of its own mass to the mass within its orbital zone. Serendipodous 09:46, 29 March 2007 (UTC)
- This is a common misconception. It's not the number of planets that some astronomers consider a problem; it's their orbits - highly eccentric, or highly inclined, or both; and with huge semi-major axes that are sometimes hard to understand in their own right. Having an object is one thing; explaining how it got there is quite another. Compared to the nearly circular orbits of everything large inside Neptune, that tells you something different has been going on. So it's partially a dynamical and formation issue as well. Spiral Wave 19:49, 28 March 2007 (UTC)
- i doubt there would be that many, but i get your point. however, i dont see why we have to not call them planets. i dont think it would be that hard to memorize them all. i can remember the 50 states. a planet is pretty much a big thing that orbits a star. if there happens to be a lot of them, so be it.
- There wouldn't be 16 planets; there be more like 1600. We just haven't found them all yet. Try getting kids to memorise all those in school. Serendipodous 04:30, 21 March 2007 (UTC)
- what the true problem is is that people are getting stuck over a definition. what you call it does not change what it is. i MY opinion, everything that directly orbits the sun and has enough mass to be round is a planet. the true root of the problem is that then there would be like 16 planets, and having a lot of planets is supposed to be bad. i dont understand why anyone thinks this way.
- Again, people forget that this is not only about Pluto. If for some reason Pluto gets back its planethood, it would mean that at least some of the other dwarf planets would also become planets. I don't think that returning to pre-2006 situation is possible. Eight or dozens of planets, but not nine.--JyriL talk 21:54, 17 March 2007 (UTC)
- Not to be difficult, but if the decision were made to redesignate, I doubt that something as minor as the numbering would stand in the way. There's no reason to renumber the following objects, no more than there is to retrieve and renumber your cheques if you have to cancel one. Worst case scenario, they could declare 134340 permanently empty ("retired"?) and move on. (Don't forget that Pluto - having been assigned a number 76 years after its discovery - isn't in chronological order anyways.) --Ckatzchatspy 08:56, 16 March 2007 (UTC)
The thing is that there are families of objects which go roughly like this IMHO
- Lumps of Ice and Rock which orbit the Sun
- Giants
- Gas Giants - Jupiter and Saturn
- Ice Giants - Uranus and Neptune
- Terrestials - Mercury, Venus, Earth and Mars
- Planetoids
- Asteroids - Ceres, Pallas, Juno, etc.
- Kupier Belt Objects - Eris, Pluto, etc.
- Comets
- Giants
The term planet itself is somewhat outdated - refering IMHO to the terrestials and giants together when there is little to connect them beyond easy visibility from Earth. If I were to plan school curriculums then this is how I would teach it - there's not much point making kids learn the names of the nine planets as abstract concepts, but learning something of the nature of the bodies as well is surely better. --Neo 11:48, 21 March 2007 (UTC)
- The "easy visibility from Earth" could well lend itself to a definition. First, let's establish two distances, the chronos (the greatest possible between Earth and Saturn), the ares (the greatest possible between Earth and Mars), and the geo (the greatest possible distance between the Sun and the Earth). How about a definition that went like this? "A planet is an object orbiting a star or stars, that is visible to an observer at a distance at 1 geo from the point being orbited. If the object in question is gaseous, it must be naked-eye visible to that observer at a distance of 1 chronos. If the object in question is rocky, it must be naked-eye visible to that observer at a distance of 1 ares." Terribly geocentric, yes, but quite in keeping with the origin of the term. El charangista 01:20, 26 April 2007 (UTC)
[edit] Recent addition
re: this addition:
Much of the work of pre-Socratic philosopher Philolaus, revolved around his struggle with the prevailing ideas surrounding the seven bodies accepted as planets during his time. When the movements of celestial objects convinced Philolaus that the world must be not only turning on its own axis but revolving around a fixed point in space, he was faced with the problem of explaining how a flat world (such as ours was thought to be) could move in this way without spilling everything on the surface into space. He came to the conclusion that the directions of up and down do not exist in space, except in that all things must fall towards the center of the universe, around which all things (including the Earth, Sun, and all the planets) must revolve. The underside of our Earth must face this fiery, central point at all times, otherwise we would fall off. This created a contradiction within the Pythagorean school of thought. Since planets, in their understanding, were composed of a fiery or ethereal matter having little or no density, they could quite easily rotate eccentric to the Earth without becoming off balance. However, the Earth was obviously made of the dense elements of Earth and Water. If there were a single Earth revolving at some distance from the center of space, the universe's center of balance would not coincide with its spatial center. Since this is the point towards which things fall, the earth must have a counter-balance of the same mass or the universe would be flung apart. This problem led Philolaus to develop idea of a Counter-Earth, a second, flat Earth, identical but opposite to ours in every way.
_____________
This addition is very interesting but it has nothing to do with the topic; the issue at hand in that section is the difference between the five planet and seven planet conception. This addition does nothing to address that. It would be better placed in the flat earth or geocentrism articles. It's also completely unsourced. Serendipodous 20:01, 16 May 2007 (UTC)
