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After having been working on the Planet article on and off for a long time, it occurs to me that there is a much better "definition of planet" section there than here. If somebody could find the time, could they add some (or all) of that information here? This article is severely lacking by comparison. _________________________________________________________________________
Actually, there really isn't a lot of information in that article that isn't here; it's just arranged differently. The "planet" subsection begins by mentioning the debate (still unresolved) convened by interested parties of the IAU, which is also mentioned at the head of this article. It then proceeds to say that the consensus they were arriving at was:
"A planet is a body that directly orbits a star, is large enough to be round because of self gravity, and is not so large that it triggers nuclear fusion in its interior."
All three of these criteria are mentioned in the article; the first two are mentioned just under the "issues and controversies" heading, the last is mentioned near the end of the "minor planets" section. That consensus definition, it appears, was illusory and news is that the IAU group are no closer to a resolution than before. Indeed the first "official" declaration by the group was completely different from the one listed in the "planet" section, so for now, until they make the truly final statement on the matter, it seems best to leave such speculation out.
The next section deals with the differences between planets and brown dwarfs, which is the topic of the third subsection of this article. Gibor Basri's definition is not really any different than the one mentioned above it. Although his work is phenomenal and this article has links to his essays on the subject, it seems premature to give credence to any one definition or theory until the final word is in from the IAU. However if you feel that this information could be better-arranged, please feel free to suggest alterations. Serendipodous 21:11, 21 December 2005 (UTC)
I consider much faster Pluto as a planet than Jupiter, Saturn, Uranus or Neptune. For me a planet is a sizable mass that is so big that it starts to appear as round, and where we can land :D. My def is much better than that of those lunatics that say Jupiter is a planet and Pluto is not. A Xanax would solve their problem. - Pedro 18:40, 1 May 2005 (UTC)
Duh. I know Pluto is slower than Jupiter. Sorry, I didn't express myself well: I wrote "has", but I meant "as". Jupiter has a different formation, just like a star is a star. What's the problem of having several more planets? If they exist I dont see where's the problem. It wont leave us with a thousand planets, but a dozen more (today). To be round a planet must have more than 360 km in diameter when it has a tendency to become round and with that size there are just a few more.-- Pedro 01:17, 26 May 2005 (UTC)
This image portrays the Moon as much smaller than it actually is. It should be edited or replaced. Pluto is actually about 2/3 the size of the Moon, not 5/6; the Earth is about 3.6 times as big as the Moon, and the picture shows it at about 4 1/2 times as big.
The problem with "planet" boils down to one's emotional investment in the term. In times long past, there were the Seven Planets. Nowadays its just another word for a class of celestial object. Arbitrariness is unavoidable, like the minimum size cutoff of 50 m for asteroids. Urhixidur 12:57, 2005 May 26 (UTC)
Regarding last comment, Mercury, Venus and Mars all have magnetic fields—I will remove the line. I also noted that Titan and Ganymede aren't as massive as Mercury. For what it's worth, I think Mercury rather than Pluto should be the cut-off point for planets (much as I have affection for Pluto...). Given that no moon in the solar system and presumably no Kuiper Belt object yet to be found is as massive as Mercury it allows for a neat line to be drawn. It may take a few years but given the finding of a KB object larger than Pluto recently, Pluto will almost certainly be downgraded. If so, we'll have 8 planets as it should be.
One other thing: the last paragraph reads really strangely. All astronomers "care about" is that the "concept" of extra-solar planets and belts of material be accepted. Extra-solar planets and potentially planet forming dust discs are no longer hypothetical. I don't think anyone doubts them as a "concept" and thus the paragraph seems useless. Marskell 07:55, 30 July 2005 (UTC)
This addition to the intro is perpetually being resurrected:
The lexical definition has changed over time, initially being an extensional definition (a list), becoming an intensional definition (the necessary and sufficient conditions for belonging to the set), and finally today in scientific use a precising definition is used which fine tunes the dictionary definition (lexical definition) of the term for the current specific issue under discussion.
I'm no expert on lexicography, but regardless, I fail to see what a paragraph about the definition of definitions has to do with planets. Also, this addition implies that there is a single definition of "planet", when none actually exists, which means it is factually inaccurate. And I'm sorry; this may be a lexicographically accurate statement, but it is poorly written. If you're going to load a paragraph with such specific jargon, you should explain what that jargon means in such a way that someone unfamiliar with your field can grasp it. If that requires that the paragraph be hundreds of words long, then the paragraph is useless. Serendipodous 18:33, 7 September 2005 (UTC)
The paragraph is not in an article about planets; it is in an article about the definition of planets. There is a difference. "What is a definition" is part of "What is the definition of a planet". So a link to definition is needed. Also, part of the problem with discussing the definition of a planet is some people come into the discussion with erroneous preconcieved notions of what a "definition" is. Another problem is that not only has the definition of planet changed, the type of definition employed has also changed.
This encyclopeedia is for everyone. Don't dumb it down. I have no doubt Wikipedia has other contents neither of us fully grasp (perhaps Navier-Stokes equations). The point of the links is so you can use them and learn. So learn and don't delete accurate relevant data just cause you can't be bothered to learn something new. It's not poorly written. It's short and to the point and has links for anyone who thinks to themself "Gee, I don't get what I just read."
"the IAU used "historical practice in accepting the eight planets that were known when the IAU was created and accepting Pluto as the ninth when it was discovered (in 1930) not long after the formation of the IAU." [1] Originally a planet was one of the permanent wandering points of light in the sky. A specific list existed that didn't change until modern times. In accepting additions to the list, the list was changed based on the necessary and sufficient conditions for belonging to the set (what you probably think of as a "real" definition) because a new object (e.g. Pluto) was discovered that was more like the current items in the list of planets than anything else known at the time. Today, we know of all manner of objects in the sky that range in tiny increments from lone electrons in space to space dust to tiny rocks to big rocks to very very big rocks, to small mooons to large planets to small stars to large stars to black holes. Scientists today carefully define their terms in their papers depending on the point they are trying to make. An object can be called an asteroid or a comet depending on what's being discussed. Same with moon or planet. Or planet vs. star. Inbetween objects are in a sense BOTH. WAS 4.250 08:52, 31 July 2005 (UTC)
The definition has changed over time. It has sometimes been an extensional definition (a list) and sometimes an intensional definition (the necessary and sufficient conditions for belonging to the set) at various points in time, and still is for many non-scientists. Today in scientific use precising definitions are used which fine tune the dictionary definition (lexical definition) of the term for the specific issue under discussion.
Better? Any futher enhancements needed? Or does this just make it worse for you? (I prefer the [first A then B then C] even if it is a gross simplification.) WAS 4.250 16:41, 31 July 2005 (UTC)
I disagree that the intro is well written. It lacks parallel structure (... [subject] has changed ..., being ..., becoming ..., and finally [second subject] is used ...). Apart from style, the problem implies a false progression of “lexical,” from “extensional” to “intensional” to “precising.” Also, “lexical definition” is initially used without explanation and later appears as a parenthetical to explain “dictionary definition.” The sentence seems to be going out of its way to modify the word “definition” as many different ways as possible, even when not saying anything new. - no-name
First, 82.45.244.104 you should create an account with a recognizable name if you want to be caretaker for articles like this. Regarding magnetic fields, I don't want to pretend to a lot of scientific knowledge I don't have but I think you've mistaken the magnetosphere for the magnetic field itself. The former is an envelope of space in which the magnetic field is dominant and through which the solar wind largly doesn't pass. The solar wind does not create the magnetic field in any sense. The magnetic field is a product of the rotation of iron in a planet's core. You may want to state that only Earth among terrestrial bodies has a substantial magnetic field. Apparently on Venus and Mars the field is extremely weak.
Regarding, potential bodies Mercury size, you are right that picking Mercury as the cutoff may be convenient but is much more arbitrary than forming into a sphere or being below nuclear fusion mass. Two ways to look at it. First, we have long devised useful measurements in which the external reference point is basically meaningless but still conventionally understandable. The foot unit is likely the length King Henry I boots. So we pick Mercury and say that's it. Eleven inches is not a foot and a body below Mercury mass is not a planet. Alternatively the IAU could pick an actual numerical marker close to Mercury size and make this the point; Merucry is 0.055 Earth masses while Pluto is more than an order of magnitude lower (Ganymede is half the amount). Thus, O.05 Earth masses could be it. I like the first alternative because it's easiest to intuitively grasp--most eight year olds know Mercury is first in line from the sun but 0.05 Earth masses is just another big number. Marskell 14:06, 31 July 2005 (UTC)
Serendipodous 18:34, 7 September 2005 (UTC)
What about a moon controversy. How can space rocks around planets be classified as moons. Shouldn't we have two types of moons? maybe moons (or secundary planets or even satellite planet) for Titan, Ganymede, Europa, our Moon and another notable moons (honestely I find moons more interresting than main planets), maybe "natural satellites" for those smaller objects (or another name for these space rocks). today all terms are applied to all objects. If we only would name bigger objects with Roman dieties, we wouldnt have today's problem with so many freaky names that no one can remember. -- Pedro 10:01, 3 August 2005 (UTC) [2] (see "New Names for Saturn's Tiniest Moons" section for definition of a moon controversy)-- Pedro 11:24, 3 August 2005 (UTC)
-- User:yisraelasper As I pointed out with the the problem of naming satellites of brown dwarfs no longer is it absolute that a satellite is a moont. The IAU is no help here as it simply avoids the term moon. I say that we should then push for the spread of the knowledge of the separation between the term satellite and moon and have it be for any planet except Mars which borders the Asteroid Belt so a special dispensation can be made for it to prevent a public outcry and still have some scientific meaning for it, that if an object would be considered a planet if what it orbits would be treated as a star or star or stellar remnant it should be considered a moon with the exception that however much what the objects orbits differs from a planet so can the moon.
I'm a bit confused by these two terms; one, I think, refers to a single, definable region of the solar system, while the other could refer to everything up to the Oort Cloud. I'm going to try and draft a section for the article that makes a distinction between these two terms. Serendipitous 10:32, 8 August 2005 (UTC)
I do know what they are, I am merely slightly confused as to how they are applied. The Wikipedia article on trans-Neptunian objects makes the distinction I made above, but a recent edit to the "Pluto controversy" took out any references to the Kuiper Belt, making me wonder if, by some people's standards, the term "Kuiper Belt" should not be used. I have edited the section with what I believe is the correct diffrentiation. If whoever first removed the term "Kuiper Belt" from the article disagrees with my decision they can post their reasons here, and, if I agree with their position, I would be happy to change what I wrote in accordance with what they think. Serendipitous 10:32, 8 August 2005 (UTC)
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Unfortunatly wikipedia is invaded by people dethroning Pluto, in every article there's a notion abouyt Pluto not being a planet, and who (disinformed ppl) reads this article starts thinking it is an asteroid. The pluto asteroid theory (which this article enforce) is not part of a major group of scientists. Althoug it seems wikipedia is full of those scientists that say Pluto is an asteroid, plz browse planetology topics in en.wikipedia to see that.
The problem is not Pluto being a planet, but the new spherical bodies not being one (like Ceres or orcus). -- Pedro 00:12, 17 August 2005 (UTC)
Definition by NASA (which I think it is the most correct): A Planet:
1. orbits the Sun (rather than a moon that orbits a planet) 2. is big enough so that its own gravity pulls it together into a sphere (it must be round)
If you read this article you are leaded to think a lot of things, and leaded to one point, Pluto isnt a planet. I think we should use info from these references also, and in their view why it is a planet. Ceres was classified as an asteroid because they couldnt see its disc, but a dot.
Planets are differentiated, if you look very carefully, by their tiny spherical shape. If you can't the tiny disc, it is a star. If you see the disc it is a planet. We know today that Ceres is spherical, then they didn’t knew because, yes, it was smaller than Mars, but with today's telescopes we can see Ceres disc.
There are stars (which burn), comets (small, and have a tail when it comes close to the sun), planets (spherical, orbit the sun) and satellites/moons (orbit a planet), and asteroids (not spherical). It is pretty clear if you classify bodies by their appearance you will notice that many are at least planetoids. Plus, see this: http://www.spacedaily.com/news/outerplanets-04b.html
I've been working on creating featured articles on planetology in the Portuguese lang. wikipedia: pt:Marte (planeta) (Mars), pt:Titã (satélite) (Titan) and pt:Tritão (satélite) (Triton) and I found very hard not to use the word "Planet" in Titan and Triton. In fact, some authors use it, so I use it occasionally, but avoiding it. Triton is a very complex planet, and it is possibly similar to Pluto. I think the definition of a planet should be the responsibility of planetary scientists. Defining a Planet just by its orbit is not a very good thing to do. The Earth compared to Jupiter is just a moon... -- Pedro 01:28, 17 August 2005 (UTC)
My contra-definition of a star: A star is any body of the galaxy that is more massive than the total mass of all of the other bodies that shine. Honestly I didnt expect that "fool" definition from a discoverer of objects in the solar system. But that's my thinking.- Pedro 16:59, 22 August 2005 (UTC)
hey what are those four rocky balls after Jupiter - We know Mars since 1930s - but we now discovered an object bigger than Mars, the Earth! these are Trans-Jupiter (Belt) Objects, the TJO's! There are four large (we have also discovered more recently, one also the size of Earth (Venus) and one even tinier (Mercury), and also a medium sized (ceres) and several other tiny rocks in a very caotic belt known as Anti-kuiper Belt. Because they are so many and that space is full or rocks, Mars will no longer be considered a planet. these four (or five) planets should be removed from Planethood. And Earth is just a big asteroid!--- Pedro 21:10, 25 January 2006 (UTC)
Please, be careful how you edit a Wikipedia page; be sure to read the whole article before you make an addition. Much of the information you posted was already mentioned and discussed in the article, in different sections; in particular, the links you posted were almost all already listed in the "External links" section at the bottom. On that subject, please stop posting massive external links in the middle of pages. If you want to post an external link, post it in the "external links" section, or indicate it with a number. Links do not have to have the full web address on the page- all you have to do is click the "Link" icon on the top of the page, and you can write a link like this: link title. Make the link title a simple number, and save a lot of room. Plus, I am assuming that English is not your first language, as much of what you wrote was grammatically confusing. It would help if you made clear what you intended to write on the discussion page before you posted it. Serendipitous 19:23, 28 August 2005 (UTC)
You might as well ask that of the whole Wikipedia project. Wikipedia articles change, sometimes fundamentally, over time. Much of the information in the articles is ephemeral; a lot of it is here one day and gone the next, replaced by something new. There is no point in referencing a Wikipedia article because the information you refer to could be gone the next day. If you are interested in a solid source for easy reference, may I suggest a rather quaint item known as a book? Serendipodous 21:36, 22 September 2005 (UTC)
In the article, it states that the cutoff for "planethood" should be "when an object becomes spherical under its own gravity". Later in that section, as well as on this discussion page, it has been stated that this criterion "conveys only that they are round". It also says in the article that "it would not only let Pluto into the planetary club, but also Ceres". If one reads the wording carefully, one sees that this is not what the criterion means. While this criterion would mean that all planets are round, it does not mean that all round objects orbiting stars would be considered planets. The phrase "under its own gravity" is the key point. This criterion therefore convey's more about mass than about shape. I'm sure there are many asteroids in the asteroid belt that just happen to be round. That does not mean that they are that way because of their own gravity. A baseball is round, but it is so because it was made that way, not because of the baseball's gravity. My point is that Ceres would not necessarily be deemed a planet by this criteron (I don't know if Ceres is actually big enough to be spherical _due to its own gravity_.. someone please clarify this point).
As an additional note, this criterion might actually say something about composition, since some bodies may require less gravity to become spherical than others depending on composition, though I do not have the expertise to know if this would be the case. I am only pointing out a flaw in the article's reasoning.
Some external links were sprinkled randomly into the article recently. I have collected them into a proper References section, but I'm not sure they really add anything to the article in the first place. Opinions? -- Doradus 14:29, 25 September 2005 (UTC)
Upa. That was me. I wrote this article a long time ago and a few days ago it suddenly occurred to me that much of what I had written had come straight out of my own head and wasn't substantiated or backed up, so I thought I'd add some references just to reassure that I wasn't just speaking personal opinions. Perhaps they don't need to be there. Serendipodous 15:03, 25 September 2005 (UTC)
I see that you have deleted them. I just thought that I should explain my "I'm not sure they really add anything" remark... They seemed to be pretty much arbitrary websites, rather than authoratative sources. Frankly, they looked like the kind of links one would find on the first page of a Google search. However, if they are authoratative sources, I have no problem retaining that References section. -- Doradus 14:19, 26 September 2005 (UTC)
Well, in all fairness, they weren't the first page...
The problem is that finding something (anything) that directly and explicitly confirms what you say on the internet is actually very difficult. I don't really like the internet as a research tool, since unless you know what you're looking for, you usually have to sift through tons of dross before you find something even remotely relevant. I still prefer books. Perhaps that is a personal flaw. Anyway, I found what looks like a far better source. Pretty much answers most of my problems. Serendipodous 15:17, 26 September 2005 (UTC)
What if only smaller bodies can have more than one spin axis. Would that not set a natural size limit to use in defining a planet? Jan Pedersen 11:02, 27 September 2005 (UTC)
I think reclassify is better, there is no ranking of heavenly bodies.-- Perfection 06:28, 4 October 2005 (UTC)
Hmm. I think, given the context, it might be better to put the word "demoted" in quotation marks, since that is a word often associated with the anti-reclassification camp. The word "reclassified" is already used in the previous sentence. Serendipodous 07:04, 4 October 2005 (UTC)
There seems to be a slight contradiction in the sentance newly added by Tompw:
"The required distance depends solely on the mass of the planet. (The further the planet is from the Sun, the further the moon needs to be from the planet)."
If the planet's distance from the Sun is a factor in the required distance, then it can't solely be related to the mass of the planet. Serendipodous 17:38, 4 November 2005 (UTC)
I have cut and pasted your addition here Anthony, because I want you to fully understand why it is incorrect to use it in this context:
Planetary systems around stars, including our own, may be comprised of not only planets but other orbiting non-stellar bodies like natural satellites, asteroids, meteoroids, comets, and cosmic dust.
This article takes as its starting point that there is no fixed definition of "planet." That's its thesis. Any attempt to say "not only of planets but..." implicitly defines a planet by saying what it is not. That sentence claims, by the way it is worded, that a planet is not a natural satellite, an asteroid, a meteroid, a comet or cosmic dust, but the whole point of the article is that, depending on what definition you use, a planet could very well be a natural satellite, an asteroid, a meteroid, a comet, or cosmic dust. There is no definition of planet, and therefore it could be any of those things. Please read the article more carefully. Serendipodous 12:35, 8 November 2005 (UTC)
You didn't phrase it that way Anthony; you said "not only of planets but..." implying that you already had a set definition of planet in your head. I fail to see where any of your list was not mentioned in the article: the ambiguity over "natural satellites" are mentioned in the "double planets" section, the ambiguity over asteroids, meteroids and comets was mentioned in the "minor planets" section, as was cosmic dust.
As for personal attacks, I do not see calling you stubborn a personal attack; it is merely an observation. And yes, I will freely admit to it myself; the difference is that you have shown, in our brief time as "collaborators" a marked inability, or unwillingness, to comprehend even the most basic thing I have said in answer to some of your edits. There are times when I wonder if we are speaking a mutually intelligable language.
But, regardless the information does deserve to be in the article; I have rephrased it and put it in a more suitable location. Serendipodous 13:04, 8 November 2005 (UTC)
"A planet is any body in the solar system that is more massive than the total mass of all of the other bodies in a similar orbit"
While this definition excludes Pluto and Sedna, 1 Ceres _is�_ bigger then rest of the asteroid belt put together, and is therefore a planet. Am I the first person to notice this? Algr 5:42, 31 December 2005 (UTC)
According to its Wikipedia article, Ceres is about half as massive as the rest of the belt. I've asked some serious scientists to confirm that, and when they get back to me I'll let you know. Serendipodous 11:15, 31 December 2005 (UTC)
in the history page. You seem to be suggesting Herschel fudged his results; I fail to see how he could have had an accurate measure of Ceres' and Vesta's sizes, given the accuracy of telescopes at the time. Also, size isn't really the point of that section; the issue is a shared orbit. Size is covered in the following section. Serendipodous 23:25, 28 January 2006 (UTC)
The comment(s) below were originally left at Talk:Definition of planet/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
There seem to bad formulations in the subsection Definition of planet#Double planets. See Talk:Definition of planet#Definition of natural satellite. Therefore the article currently doesn't deserve FA rating. Andres 13:20, 27 August 2006 (UTC) |
Last edited at 13:20, 27 August 2006 (UTC). Substituted at 20:23, 2 May 2016 (UTC)
![]() | This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 | Archive 2 | Archive 3 | → | Archive 5 |
After having been working on the Planet article on and off for a long time, it occurs to me that there is a much better "definition of planet" section there than here. If somebody could find the time, could they add some (or all) of that information here? This article is severely lacking by comparison. _________________________________________________________________________
Actually, there really isn't a lot of information in that article that isn't here; it's just arranged differently. The "planet" subsection begins by mentioning the debate (still unresolved) convened by interested parties of the IAU, which is also mentioned at the head of this article. It then proceeds to say that the consensus they were arriving at was:
"A planet is a body that directly orbits a star, is large enough to be round because of self gravity, and is not so large that it triggers nuclear fusion in its interior."
All three of these criteria are mentioned in the article; the first two are mentioned just under the "issues and controversies" heading, the last is mentioned near the end of the "minor planets" section. That consensus definition, it appears, was illusory and news is that the IAU group are no closer to a resolution than before. Indeed the first "official" declaration by the group was completely different from the one listed in the "planet" section, so for now, until they make the truly final statement on the matter, it seems best to leave such speculation out.
The next section deals with the differences between planets and brown dwarfs, which is the topic of the third subsection of this article. Gibor Basri's definition is not really any different than the one mentioned above it. Although his work is phenomenal and this article has links to his essays on the subject, it seems premature to give credence to any one definition or theory until the final word is in from the IAU. However if you feel that this information could be better-arranged, please feel free to suggest alterations. Serendipodous 21:11, 21 December 2005 (UTC)
I consider much faster Pluto as a planet than Jupiter, Saturn, Uranus or Neptune. For me a planet is a sizable mass that is so big that it starts to appear as round, and where we can land :D. My def is much better than that of those lunatics that say Jupiter is a planet and Pluto is not. A Xanax would solve their problem. - Pedro 18:40, 1 May 2005 (UTC)
Duh. I know Pluto is slower than Jupiter. Sorry, I didn't express myself well: I wrote "has", but I meant "as". Jupiter has a different formation, just like a star is a star. What's the problem of having several more planets? If they exist I dont see where's the problem. It wont leave us with a thousand planets, but a dozen more (today). To be round a planet must have more than 360 km in diameter when it has a tendency to become round and with that size there are just a few more.-- Pedro 01:17, 26 May 2005 (UTC)
This image portrays the Moon as much smaller than it actually is. It should be edited or replaced. Pluto is actually about 2/3 the size of the Moon, not 5/6; the Earth is about 3.6 times as big as the Moon, and the picture shows it at about 4 1/2 times as big.
The problem with "planet" boils down to one's emotional investment in the term. In times long past, there were the Seven Planets. Nowadays its just another word for a class of celestial object. Arbitrariness is unavoidable, like the minimum size cutoff of 50 m for asteroids. Urhixidur 12:57, 2005 May 26 (UTC)
Regarding last comment, Mercury, Venus and Mars all have magnetic fields—I will remove the line. I also noted that Titan and Ganymede aren't as massive as Mercury. For what it's worth, I think Mercury rather than Pluto should be the cut-off point for planets (much as I have affection for Pluto...). Given that no moon in the solar system and presumably no Kuiper Belt object yet to be found is as massive as Mercury it allows for a neat line to be drawn. It may take a few years but given the finding of a KB object larger than Pluto recently, Pluto will almost certainly be downgraded. If so, we'll have 8 planets as it should be.
One other thing: the last paragraph reads really strangely. All astronomers "care about" is that the "concept" of extra-solar planets and belts of material be accepted. Extra-solar planets and potentially planet forming dust discs are no longer hypothetical. I don't think anyone doubts them as a "concept" and thus the paragraph seems useless. Marskell 07:55, 30 July 2005 (UTC)
This addition to the intro is perpetually being resurrected:
The lexical definition has changed over time, initially being an extensional definition (a list), becoming an intensional definition (the necessary and sufficient conditions for belonging to the set), and finally today in scientific use a precising definition is used which fine tunes the dictionary definition (lexical definition) of the term for the current specific issue under discussion.
I'm no expert on lexicography, but regardless, I fail to see what a paragraph about the definition of definitions has to do with planets. Also, this addition implies that there is a single definition of "planet", when none actually exists, which means it is factually inaccurate. And I'm sorry; this may be a lexicographically accurate statement, but it is poorly written. If you're going to load a paragraph with such specific jargon, you should explain what that jargon means in such a way that someone unfamiliar with your field can grasp it. If that requires that the paragraph be hundreds of words long, then the paragraph is useless. Serendipodous 18:33, 7 September 2005 (UTC)
The paragraph is not in an article about planets; it is in an article about the definition of planets. There is a difference. "What is a definition" is part of "What is the definition of a planet". So a link to definition is needed. Also, part of the problem with discussing the definition of a planet is some people come into the discussion with erroneous preconcieved notions of what a "definition" is. Another problem is that not only has the definition of planet changed, the type of definition employed has also changed.
This encyclopeedia is for everyone. Don't dumb it down. I have no doubt Wikipedia has other contents neither of us fully grasp (perhaps Navier-Stokes equations). The point of the links is so you can use them and learn. So learn and don't delete accurate relevant data just cause you can't be bothered to learn something new. It's not poorly written. It's short and to the point and has links for anyone who thinks to themself "Gee, I don't get what I just read."
"the IAU used "historical practice in accepting the eight planets that were known when the IAU was created and accepting Pluto as the ninth when it was discovered (in 1930) not long after the formation of the IAU." [1] Originally a planet was one of the permanent wandering points of light in the sky. A specific list existed that didn't change until modern times. In accepting additions to the list, the list was changed based on the necessary and sufficient conditions for belonging to the set (what you probably think of as a "real" definition) because a new object (e.g. Pluto) was discovered that was more like the current items in the list of planets than anything else known at the time. Today, we know of all manner of objects in the sky that range in tiny increments from lone electrons in space to space dust to tiny rocks to big rocks to very very big rocks, to small mooons to large planets to small stars to large stars to black holes. Scientists today carefully define their terms in their papers depending on the point they are trying to make. An object can be called an asteroid or a comet depending on what's being discussed. Same with moon or planet. Or planet vs. star. Inbetween objects are in a sense BOTH. WAS 4.250 08:52, 31 July 2005 (UTC)
The definition has changed over time. It has sometimes been an extensional definition (a list) and sometimes an intensional definition (the necessary and sufficient conditions for belonging to the set) at various points in time, and still is for many non-scientists. Today in scientific use precising definitions are used which fine tune the dictionary definition (lexical definition) of the term for the specific issue under discussion.
Better? Any futher enhancements needed? Or does this just make it worse for you? (I prefer the [first A then B then C] even if it is a gross simplification.) WAS 4.250 16:41, 31 July 2005 (UTC)
I disagree that the intro is well written. It lacks parallel structure (... [subject] has changed ..., being ..., becoming ..., and finally [second subject] is used ...). Apart from style, the problem implies a false progression of “lexical,” from “extensional” to “intensional” to “precising.” Also, “lexical definition” is initially used without explanation and later appears as a parenthetical to explain “dictionary definition.” The sentence seems to be going out of its way to modify the word “definition” as many different ways as possible, even when not saying anything new. - no-name
First, 82.45.244.104 you should create an account with a recognizable name if you want to be caretaker for articles like this. Regarding magnetic fields, I don't want to pretend to a lot of scientific knowledge I don't have but I think you've mistaken the magnetosphere for the magnetic field itself. The former is an envelope of space in which the magnetic field is dominant and through which the solar wind largly doesn't pass. The solar wind does not create the magnetic field in any sense. The magnetic field is a product of the rotation of iron in a planet's core. You may want to state that only Earth among terrestrial bodies has a substantial magnetic field. Apparently on Venus and Mars the field is extremely weak.
Regarding, potential bodies Mercury size, you are right that picking Mercury as the cutoff may be convenient but is much more arbitrary than forming into a sphere or being below nuclear fusion mass. Two ways to look at it. First, we have long devised useful measurements in which the external reference point is basically meaningless but still conventionally understandable. The foot unit is likely the length King Henry I boots. So we pick Mercury and say that's it. Eleven inches is not a foot and a body below Mercury mass is not a planet. Alternatively the IAU could pick an actual numerical marker close to Mercury size and make this the point; Merucry is 0.055 Earth masses while Pluto is more than an order of magnitude lower (Ganymede is half the amount). Thus, O.05 Earth masses could be it. I like the first alternative because it's easiest to intuitively grasp--most eight year olds know Mercury is first in line from the sun but 0.05 Earth masses is just another big number. Marskell 14:06, 31 July 2005 (UTC)
Serendipodous 18:34, 7 September 2005 (UTC)
What about a moon controversy. How can space rocks around planets be classified as moons. Shouldn't we have two types of moons? maybe moons (or secundary planets or even satellite planet) for Titan, Ganymede, Europa, our Moon and another notable moons (honestely I find moons more interresting than main planets), maybe "natural satellites" for those smaller objects (or another name for these space rocks). today all terms are applied to all objects. If we only would name bigger objects with Roman dieties, we wouldnt have today's problem with so many freaky names that no one can remember. -- Pedro 10:01, 3 August 2005 (UTC) [2] (see "New Names for Saturn's Tiniest Moons" section for definition of a moon controversy)-- Pedro 11:24, 3 August 2005 (UTC)
-- User:yisraelasper As I pointed out with the the problem of naming satellites of brown dwarfs no longer is it absolute that a satellite is a moont. The IAU is no help here as it simply avoids the term moon. I say that we should then push for the spread of the knowledge of the separation between the term satellite and moon and have it be for any planet except Mars which borders the Asteroid Belt so a special dispensation can be made for it to prevent a public outcry and still have some scientific meaning for it, that if an object would be considered a planet if what it orbits would be treated as a star or star or stellar remnant it should be considered a moon with the exception that however much what the objects orbits differs from a planet so can the moon.
I'm a bit confused by these two terms; one, I think, refers to a single, definable region of the solar system, while the other could refer to everything up to the Oort Cloud. I'm going to try and draft a section for the article that makes a distinction between these two terms. Serendipitous 10:32, 8 August 2005 (UTC)
I do know what they are, I am merely slightly confused as to how they are applied. The Wikipedia article on trans-Neptunian objects makes the distinction I made above, but a recent edit to the "Pluto controversy" took out any references to the Kuiper Belt, making me wonder if, by some people's standards, the term "Kuiper Belt" should not be used. I have edited the section with what I believe is the correct diffrentiation. If whoever first removed the term "Kuiper Belt" from the article disagrees with my decision they can post their reasons here, and, if I agree with their position, I would be happy to change what I wrote in accordance with what they think. Serendipitous 10:32, 8 August 2005 (UTC)
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Unfortunatly wikipedia is invaded by people dethroning Pluto, in every article there's a notion abouyt Pluto not being a planet, and who (disinformed ppl) reads this article starts thinking it is an asteroid. The pluto asteroid theory (which this article enforce) is not part of a major group of scientists. Althoug it seems wikipedia is full of those scientists that say Pluto is an asteroid, plz browse planetology topics in en.wikipedia to see that.
The problem is not Pluto being a planet, but the new spherical bodies not being one (like Ceres or orcus). -- Pedro 00:12, 17 August 2005 (UTC)
Definition by NASA (which I think it is the most correct): A Planet:
1. orbits the Sun (rather than a moon that orbits a planet) 2. is big enough so that its own gravity pulls it together into a sphere (it must be round)
If you read this article you are leaded to think a lot of things, and leaded to one point, Pluto isnt a planet. I think we should use info from these references also, and in their view why it is a planet. Ceres was classified as an asteroid because they couldnt see its disc, but a dot.
Planets are differentiated, if you look very carefully, by their tiny spherical shape. If you can't the tiny disc, it is a star. If you see the disc it is a planet. We know today that Ceres is spherical, then they didn’t knew because, yes, it was smaller than Mars, but with today's telescopes we can see Ceres disc.
There are stars (which burn), comets (small, and have a tail when it comes close to the sun), planets (spherical, orbit the sun) and satellites/moons (orbit a planet), and asteroids (not spherical). It is pretty clear if you classify bodies by their appearance you will notice that many are at least planetoids. Plus, see this: http://www.spacedaily.com/news/outerplanets-04b.html
I've been working on creating featured articles on planetology in the Portuguese lang. wikipedia: pt:Marte (planeta) (Mars), pt:Titã (satélite) (Titan) and pt:Tritão (satélite) (Triton) and I found very hard not to use the word "Planet" in Titan and Triton. In fact, some authors use it, so I use it occasionally, but avoiding it. Triton is a very complex planet, and it is possibly similar to Pluto. I think the definition of a planet should be the responsibility of planetary scientists. Defining a Planet just by its orbit is not a very good thing to do. The Earth compared to Jupiter is just a moon... -- Pedro 01:28, 17 August 2005 (UTC)
My contra-definition of a star: A star is any body of the galaxy that is more massive than the total mass of all of the other bodies that shine. Honestly I didnt expect that "fool" definition from a discoverer of objects in the solar system. But that's my thinking.- Pedro 16:59, 22 August 2005 (UTC)
hey what are those four rocky balls after Jupiter - We know Mars since 1930s - but we now discovered an object bigger than Mars, the Earth! these are Trans-Jupiter (Belt) Objects, the TJO's! There are four large (we have also discovered more recently, one also the size of Earth (Venus) and one even tinier (Mercury), and also a medium sized (ceres) and several other tiny rocks in a very caotic belt known as Anti-kuiper Belt. Because they are so many and that space is full or rocks, Mars will no longer be considered a planet. these four (or five) planets should be removed from Planethood. And Earth is just a big asteroid!--- Pedro 21:10, 25 January 2006 (UTC)
Please, be careful how you edit a Wikipedia page; be sure to read the whole article before you make an addition. Much of the information you posted was already mentioned and discussed in the article, in different sections; in particular, the links you posted were almost all already listed in the "External links" section at the bottom. On that subject, please stop posting massive external links in the middle of pages. If you want to post an external link, post it in the "external links" section, or indicate it with a number. Links do not have to have the full web address on the page- all you have to do is click the "Link" icon on the top of the page, and you can write a link like this: link title. Make the link title a simple number, and save a lot of room. Plus, I am assuming that English is not your first language, as much of what you wrote was grammatically confusing. It would help if you made clear what you intended to write on the discussion page before you posted it. Serendipitous 19:23, 28 August 2005 (UTC)
You might as well ask that of the whole Wikipedia project. Wikipedia articles change, sometimes fundamentally, over time. Much of the information in the articles is ephemeral; a lot of it is here one day and gone the next, replaced by something new. There is no point in referencing a Wikipedia article because the information you refer to could be gone the next day. If you are interested in a solid source for easy reference, may I suggest a rather quaint item known as a book? Serendipodous 21:36, 22 September 2005 (UTC)
In the article, it states that the cutoff for "planethood" should be "when an object becomes spherical under its own gravity". Later in that section, as well as on this discussion page, it has been stated that this criterion "conveys only that they are round". It also says in the article that "it would not only let Pluto into the planetary club, but also Ceres". If one reads the wording carefully, one sees that this is not what the criterion means. While this criterion would mean that all planets are round, it does not mean that all round objects orbiting stars would be considered planets. The phrase "under its own gravity" is the key point. This criterion therefore convey's more about mass than about shape. I'm sure there are many asteroids in the asteroid belt that just happen to be round. That does not mean that they are that way because of their own gravity. A baseball is round, but it is so because it was made that way, not because of the baseball's gravity. My point is that Ceres would not necessarily be deemed a planet by this criteron (I don't know if Ceres is actually big enough to be spherical _due to its own gravity_.. someone please clarify this point).
As an additional note, this criterion might actually say something about composition, since some bodies may require less gravity to become spherical than others depending on composition, though I do not have the expertise to know if this would be the case. I am only pointing out a flaw in the article's reasoning.
Some external links were sprinkled randomly into the article recently. I have collected them into a proper References section, but I'm not sure they really add anything to the article in the first place. Opinions? -- Doradus 14:29, 25 September 2005 (UTC)
Upa. That was me. I wrote this article a long time ago and a few days ago it suddenly occurred to me that much of what I had written had come straight out of my own head and wasn't substantiated or backed up, so I thought I'd add some references just to reassure that I wasn't just speaking personal opinions. Perhaps they don't need to be there. Serendipodous 15:03, 25 September 2005 (UTC)
I see that you have deleted them. I just thought that I should explain my "I'm not sure they really add anything" remark... They seemed to be pretty much arbitrary websites, rather than authoratative sources. Frankly, they looked like the kind of links one would find on the first page of a Google search. However, if they are authoratative sources, I have no problem retaining that References section. -- Doradus 14:19, 26 September 2005 (UTC)
Well, in all fairness, they weren't the first page...
The problem is that finding something (anything) that directly and explicitly confirms what you say on the internet is actually very difficult. I don't really like the internet as a research tool, since unless you know what you're looking for, you usually have to sift through tons of dross before you find something even remotely relevant. I still prefer books. Perhaps that is a personal flaw. Anyway, I found what looks like a far better source. Pretty much answers most of my problems. Serendipodous 15:17, 26 September 2005 (UTC)
What if only smaller bodies can have more than one spin axis. Would that not set a natural size limit to use in defining a planet? Jan Pedersen 11:02, 27 September 2005 (UTC)
I think reclassify is better, there is no ranking of heavenly bodies.-- Perfection 06:28, 4 October 2005 (UTC)
Hmm. I think, given the context, it might be better to put the word "demoted" in quotation marks, since that is a word often associated with the anti-reclassification camp. The word "reclassified" is already used in the previous sentence. Serendipodous 07:04, 4 October 2005 (UTC)
There seems to be a slight contradiction in the sentance newly added by Tompw:
"The required distance depends solely on the mass of the planet. (The further the planet is from the Sun, the further the moon needs to be from the planet)."
If the planet's distance from the Sun is a factor in the required distance, then it can't solely be related to the mass of the planet. Serendipodous 17:38, 4 November 2005 (UTC)
I have cut and pasted your addition here Anthony, because I want you to fully understand why it is incorrect to use it in this context:
Planetary systems around stars, including our own, may be comprised of not only planets but other orbiting non-stellar bodies like natural satellites, asteroids, meteoroids, comets, and cosmic dust.
This article takes as its starting point that there is no fixed definition of "planet." That's its thesis. Any attempt to say "not only of planets but..." implicitly defines a planet by saying what it is not. That sentence claims, by the way it is worded, that a planet is not a natural satellite, an asteroid, a meteroid, a comet or cosmic dust, but the whole point of the article is that, depending on what definition you use, a planet could very well be a natural satellite, an asteroid, a meteroid, a comet, or cosmic dust. There is no definition of planet, and therefore it could be any of those things. Please read the article more carefully. Serendipodous 12:35, 8 November 2005 (UTC)
You didn't phrase it that way Anthony; you said "not only of planets but..." implying that you already had a set definition of planet in your head. I fail to see where any of your list was not mentioned in the article: the ambiguity over "natural satellites" are mentioned in the "double planets" section, the ambiguity over asteroids, meteroids and comets was mentioned in the "minor planets" section, as was cosmic dust.
As for personal attacks, I do not see calling you stubborn a personal attack; it is merely an observation. And yes, I will freely admit to it myself; the difference is that you have shown, in our brief time as "collaborators" a marked inability, or unwillingness, to comprehend even the most basic thing I have said in answer to some of your edits. There are times when I wonder if we are speaking a mutually intelligable language.
But, regardless the information does deserve to be in the article; I have rephrased it and put it in a more suitable location. Serendipodous 13:04, 8 November 2005 (UTC)
"A planet is any body in the solar system that is more massive than the total mass of all of the other bodies in a similar orbit"
While this definition excludes Pluto and Sedna, 1 Ceres _is�_ bigger then rest of the asteroid belt put together, and is therefore a planet. Am I the first person to notice this? Algr 5:42, 31 December 2005 (UTC)
According to its Wikipedia article, Ceres is about half as massive as the rest of the belt. I've asked some serious scientists to confirm that, and when they get back to me I'll let you know. Serendipodous 11:15, 31 December 2005 (UTC)
in the history page. You seem to be suggesting Herschel fudged his results; I fail to see how he could have had an accurate measure of Ceres' and Vesta's sizes, given the accuracy of telescopes at the time. Also, size isn't really the point of that section; the issue is a shared orbit. Size is covered in the following section. Serendipodous 23:25, 28 January 2006 (UTC)
The comment(s) below were originally left at Talk:Definition of planet/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
There seem to bad formulations in the subsection Definition of planet#Double planets. See Talk:Definition of planet#Definition of natural satellite. Therefore the article currently doesn't deserve FA rating. Andres 13:20, 27 August 2006 (UTC) |
Last edited at 13:20, 27 August 2006 (UTC). Substituted at 20:23, 2 May 2016 (UTC)