![]() | 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 4 | Archive 5 | Archive 6 |
This archive is a holding area for good content that has not been sourced, or that no longer fits the article in its current form.
"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. "
However, deciding which objects in the Solar System are spheroid is more complicated than it seems. In mathematical terms, spheroids consist of an ellipse rotated around one axis. Consequently they have two axes of equal length and one that is either longer or shorter; they resemble spheres that have been deformed (by stretching or squashing) in one dimension. A section through one axis will produce a circle, and a section through the other two axes will produce an ellipse. [1]
All spheroids, however, have the points on their surfaces joined by smooth curves (which form the elliptical or circular sections). On a topographically irregular body this can only be an approximation; however, taking such irregularity into account, a definite contrast exists between bodies, such as Enceladus, which are essentially spheroidal, and irregular bodies, like Neptune's moon Proteus, whose limbs do not show smooth curvature. [2]
If one uses this mathematical basis to define a spheroid, then the boundary between spheroidal and irregular objects within the Solar System frays noticeably, as this table illustrates:
Object | Dimensions (km) | Mass (1019 kg) | Density (g/cm³) [d] | Shape |
---|---|---|---|---|
Ceres | 975 × 909 | 95 | 2.08 | Spheroid |
4 Vesta | 578 × 560 × 478 | 27 | 3.4 | Spheroid |
2 Pallas | 570 × 525 × 500 | 22 | 2.8 | Irregular |
Enceladus | 513.2 × 502.8 × 496.6 | 10.8 | 1.61 | Spheroid |
10 Hygiea | 500 × 385 × 350 | 10 | 2.76 | Irregular |
Miranda | 480 × 468.4 × 465.8 | 6.59 | 1.20 | Spheroid |
Proteus | 436 × 416 × 402 | 5.0 | 1.3 | Irregular |
Mimas | 414.8 × 394.4 × 381.4 | 3.84 | 1.17 | Spheroid |
511 Davida | 326.1 | 3.6 | 2.0 | Irregular |
704 Interamnia | 316.6 | 3.3 | 2.0? | Irregular |
Nereid | 340 | 3.1 | ? | Irregular |
3 Juno | 290 × 240 × 190 | 3.0 | 3.4 | Irregular |
Plainly, there is no clear mass or size boundary dividing those objects in the Solar System which could be considered "spheroids" and those which are obviously irregular. The irregular objects Pallas, Hygeia and Proteus are all larger than regular objects, such as Miranda and Mimas. Also, as demonstrated by the dimensions listed in the table, the term "spheroid" is, in any case, fairly loose. Vesta, by the above formulation, could be considered either a spheroid or irregular. (see image)
The new diagram listing the changing numbers of planets is quite nice, but it does contradict the article slightly. Galileo considered his four moons "planets", though I don't know yet whether this term was widely used for them, or for how long. Until we sort this out it might be a good idea to take the diagram down for now. I'll place it here until I can get some better information.
Serendipodous 09:30, 22 February 2007 (UTC)
The picture comparing the sizes of Pluto with the Earth, the Moon and other KBOs suggests a false qualitative difference between Earth and the other objects. It is important to counter this with the observation that planets come in a huge range of sizes. The differences between Earth and Jupiter are much greater then the differences between Earth and Pluto, and that is important to deciding what a planet is. Algr 04:29, 15 July 2006 (UTC)
Serendipodous 07:43, 15 July 2006 (UTC)
Thank you! I believe this is the first time I have seen such a statement in print, and I feel vindicated. I definitely agree (disclaimer: I'm not an astronomer). When I was about 8 years old I got interested in astronomy. It seemed obvious to me from the descriptions of Jupiter and Saturn that they were unignited stars (in spite of the presence of significant amounts of methane). I've kept this opinion through the intervening 55 years, in spite of increases in my knowledge about these planets. And I would be very much surprised indeed to learn that either planet had a rocky or metallic core.
In these cases, at least, I think it is clear that an object can be viewed (and called) both a planet and star at the same time. David spector ( talk) 16:18, 6 May 2009 (UTC)
I think that, since the IAU and many astronomers insist that planets must be in orbit around the Sun, we need to coin a new word for planet-like objects in orbit around other stars.
Either that, or we should stop being so provincial and drop the requirement that a planet must orbit the Sun. We should refer to the Sun's planets as "the Sun's planets" instead of "the planets".
If we choose neither of these alternatives, as is currently the case with many astronomers, then we are forced to discuss extrasolar planets as "planets" (in quotes), since they do not fit the definition of a planet. This is unnecessarily awkward, and can only become more awkward over time as the resolution of imaging of extrasolar planets improves and the possibility of travel to them from Earth increases away from zero. David spector ( talk) 16:30, 6 May 2009 (UTC)
I really do appreciate your plaudits and enthusiasm, however, I must stress that Wikipedia is not an internet discussion forum. The talk page is really more for discussing how to improve the article. If you're interested in discussing astronomy, I can recommend the Bad Astronomy/Universe Today forum, which is frequented by many astronomers. Serendi pod ous 16:39, 6 May 2009 (UTC)
I appreciate that this is not an astronomical forum, but this article uses contradictory terms (a planet must orbit the sun but an extrasolar planet is presumably something orbiting some other star). In the absence of a defined term, the article uses a previously defined term to describe something that has been excluded by that definition. To my mind, totally unacceptable for an encyclopaedia. To use an analogy, it is akin to saying that an antipodean dog is not a dog. The problem is exacerbated because the article itself is about the definition of a planet. If this is considered the pinnacle of Wikipedia, then I am disappointed. Malchemist ( talk) 07:27, 31 July 2011 (UTC)
Under the section "Sattelites": "When Copernicus placed the Earth among the planets, he also placed the Moon in orbit around the Earth, making the Moon the first natural satellite to be discovered." "Discovered" is possibly a misplaced term here, since we're talking about an object that has arguably been observed by many lifeforms in detail over its history. I like the term "identified" better, but I wanted to run it past the talk page here. Stotan ( talk) 03:20, 7 May 2009 (UTC)
Moved discussion to talk page as per WP:NOTFORUM
Fair enough, but there is a genuinely relevant point here. The concept of "discovery" is simply not defined. Therefore infoboxes giving dates &c violate NPOV by giving special prominence to 1 POV. This applies to a lot of other stuff in infoboxes too. Peter jackson ( talk) 11:06, 5 June 2009 (UTC)
Hi,
Helping to translate the french version of this article, it appears that the quotation from Alexander von Humboldt which supposed to be in Cosmos couldn't be found in the given link. Any information on this ( pages, traductor, edition) would be appreciated.
TIA.@+ --
90.8.76.43 (
talk)
13:17, 18 May 2009 (UTC)
It's there. Unfortunately I can't provide a direct link to the paragraph because Wiki can't handle the URL and won't accept tinyurls. When you click onto the book's hyperlink, just type "unwandering orbs" into the "search this book" engine. It will say it can't find it, but then just click "search all volumes" and there it is, in that same book. Serendi pod ous 15:13, 18 May 2009 (UTC)
What does "larger by a factor of 0.33" mean? Sounds like smaller to me. Peter jackson ( talk) 10:44, 15 July 2009 (UTC)
Do Extrasolar planets (planets in other solar systems) fit in with the same definition as planets in our solar system, except "orbits the Sun" becomes "orbits a sun"? Jezzamon ( talk) 05:37, 27 August 2009 (UTC)
The sources seem to cover 2006 to 2008 with a few earlier dated sources for earlier philosophizing around language and term creation. Is the debate dead, or is it just that the wikipedians have gotten enough of a hot topic? Those of you who are professionals might know, AFAIK amateurs generally just accept the definitions that professionals claim. ... said: Rursus ( mbork³) 08:44, 2 October 2009 (UTC)
Discussion of the debate should include mention of the Great Planet Debate, organized by professional astronomers who reject the IAU definition, held at the Johns Hopkins University Applied Physics Lab in August 2008. Audio transcripts are available here: http://gpd.jhuapl.edu
This two-and-a-half day conference addressed not just Pluto and dwarf planets but also borderline objects such as protoplants Vesta and Pallas, exoplanets, brown dwarfs and the boundary between stars and the upper limit of planets, and teaching the controversy. Stern, Levison, and many other professional astronomers took part in panel discussions on these issues. It is noteworthy that Stern continues to refer to Pluto as a planet in his regular New Horizons update and that he and many planetary scientists have decided to simply ignore the IAU entirely. In talking about the discovery of Pluto's fourth moon, Stern said, "I believe that most planetary scientists know it's a planet, and we don't need the IAU to tell us it is": http://www.time.com/time/health/article/0,8599,2084606,00.html There is some thought that planetary scientists might formally break with the IAU and start their own professional organization. — Preceding unsigned comment added by Laurele ( talk • contribs) 21:53, 31 July 2011 (UTC)
Does the astronomical community have a formal definition for two planets orbiting a common center of mass like the Earth or moon, but of equal size? e.g. Two earth sized planets. The example of Pluto and charon is an example, although they are now called dwarf planets —Preceding unsigned comment added by 98.219.220.143 ( talk) 17:34, 16 May 2010 (UTC)
The section makes it sound like Sykes said the bit about Pluto being a potential planet in a different orbit, but that isn't in the reference, and we shouldn't be implying that he did. Sykes also didn't say the bit about Mars "therefore be surrounded by objects of similar mass", which is just wrong anyway (it would be surrounded, but the objects don't have to be of similar mass). Whether or not the isolated Pluto would be a planet depends on the definition "clearing..."; for example, a definition based on the Stern-Levison λ might still exclude it if the definition (like the IAU's handwaving) says that the object must clear the region, not just that the object currently inhabits in a clear region (hello Sedna!). However, I suspect we could find some reference for that argument. Finally, I don't think "ambiguous" is the right word here: with a reasonable definition, there's nothing ambiguous about whether an object is a planet or not. I left it in the first instance, but removed it from the Sykes paraphrase since that's not the expression used in the reference. Tbayboy ( talk) 00:08, 4 January 2011 (UTC)
Since editing is closed, could the first paragraphs be changed to say "pluto and transneptunian objects" rather than pluto and other transneptunian objects, since pluto isn't clearly transneptunian. —Preceding unsigned comment added by 69.180.134.188 ( talk) 05:34, 5 April 2011 (UTC)
This section is incorrect: per the IAU press release, the H=+1 criterion is not about "classifying" the object, but only about naming it, and there is no "demand" that an object meet this criterion to be named as a plutoid. This is explained well in the main article. Brown's objection (in his blog) is based on his own mis-reading, which is pointed out in one of the comments on the referenced blog page. I thought about fixing the first sentence, but then it becomes clear that this is not really a controversy but a misunderstanding, and the blog comment suggests it may have been cleared up (I didn't see anything more about it by Brown one way or the other, so can't say for sure). The whole section is then reduced to insignificance, so I took the bold to heart and nuked it. If it's to be revived, then it should be fixed to indicate what the IAU actually said, in addition to the misunderstanding that lead to the controversy. Tbayboy ( talk) 18:42, 9 April 2011 (UTC)
The language of the first two paragraphs is torturous. I'd rewrite it if editing was allowed, like this: (absolute minimum to stop my eyes bleeding when I read it)
Since the word was coined by the ancient Greeks, the definition of planet has included many things now regarded as distinct, often simultaneously. In the past the use of the term was never strict and its meaning has altered to include or exclude a variety of different objects, from the Sun and the Moon to satellites and asteroids.
By the end of the 19th century, the word planet had, without being formally defined, come to cover a smaller range of objects. It only applied to objects in the Solar System; a number small enough that any differences could be dealt with on an individual basis. After 1992 however, astronomers began to discover many additional objects beyond the orbit of Neptune, as well as hundreds of objects orbiting other stars. These discoveries not only increased the number of potential planets, but also expanded their variety. Some were nearly large enough to be stars, while others were smaller than Earth's moon. These discoveries challenged long-perceived notions of what a planet could be. — Preceding unsigned comment added by 125.237.82.60 ( talk) 10:11, 31 July 2011 (UTC)
I request the author to include Aryabhata's works and inferences to the list of astronomers (Planets in antiquity section). For more information, please see Aryabhata
Thank you,
Funkfan 08:04, 3 August 2011 (UTC)Asatya82 — Preceding
unsigned comment added by
Asatya82 (
talk •
contribs)
Is the reason that there was no improved IAU definition of planets that they wanted to pass such a decision with a large majority, but couldn't come to an agreement yet? I hope it's not that they think the current definitions are OK, because they're clearly not. For example the definition of extrasolar planet states the lower mass limit for an object to be an extrasolar planet is the same as in the Solar System... but there was no such limit given. Neither for dwarf planets nor for regular planets. There would have been no harm done if the upper limit for extrasolar planets was also applied to the Solar System, but that wasn't done either. It's like they're hiding everything behind smoke and mirrors and make up the results as they go.
It would be relatively easy to come up with criteria that could decide if a newly discovered body is a planet or not. But they didn't do it. Why? What for example is wrong with the following?
1. A planetary mass object is an object with a mass between the agreed mass limit needed for hydrostatic equilibrium (5×1020kg) and the agreed mass limit needed for deuterium fusion (2.5×1028kg). (Both limits might be set lower since the first would exclude Pallas and Vesta which are remaining protoplanets and the second doesn't take into account that objects with high metallicity could allow deuterium fusion at a lower mass)
2. A planet is a planetary mass object on an orbit around at least one star that also has the capability of clearing its orbit (per Stern-Levison criteria. The difference is you only need to know mass and orbital period of the object (and the star of course), whereas with Soter's criteria you'd need to know everything about the system).
3. A dwarf planet (I prefer mesoplanet) is a planetary mass object on an orbit around at least one star that doesn't fulfill the Stern-Levison criteria.
More definitions could be added to account for other types of planetary mass objects. I prefer "planetar" for those that don't orbit any star - regardless if they were formed by themselves or in a system of which they were later ejected. Also, I'd like "moon" to mean a planetary mass object that orbits a planet (since the prototype object Luna is just that) - smaller bodies would just keep being "satellites". (If you don't like to have 60 planets of which most are small, why would you allow 60 moons of which most are tiny?)
Any ideas why the IAU doesn't come up with something like that? Ambi Valent ( talk) 00:25, 19 January 2013 (UTC)
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![]() | 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 4 | Archive 5 | Archive 6 |
This archive is a holding area for good content that has not been sourced, or that no longer fits the article in its current form.
"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. "
However, deciding which objects in the Solar System are spheroid is more complicated than it seems. In mathematical terms, spheroids consist of an ellipse rotated around one axis. Consequently they have two axes of equal length and one that is either longer or shorter; they resemble spheres that have been deformed (by stretching or squashing) in one dimension. A section through one axis will produce a circle, and a section through the other two axes will produce an ellipse. [1]
All spheroids, however, have the points on their surfaces joined by smooth curves (which form the elliptical or circular sections). On a topographically irregular body this can only be an approximation; however, taking such irregularity into account, a definite contrast exists between bodies, such as Enceladus, which are essentially spheroidal, and irregular bodies, like Neptune's moon Proteus, whose limbs do not show smooth curvature. [2]
If one uses this mathematical basis to define a spheroid, then the boundary between spheroidal and irregular objects within the Solar System frays noticeably, as this table illustrates:
Object | Dimensions (km) | Mass (1019 kg) | Density (g/cm³) [d] | Shape |
---|---|---|---|---|
Ceres | 975 × 909 | 95 | 2.08 | Spheroid |
4 Vesta | 578 × 560 × 478 | 27 | 3.4 | Spheroid |
2 Pallas | 570 × 525 × 500 | 22 | 2.8 | Irregular |
Enceladus | 513.2 × 502.8 × 496.6 | 10.8 | 1.61 | Spheroid |
10 Hygiea | 500 × 385 × 350 | 10 | 2.76 | Irregular |
Miranda | 480 × 468.4 × 465.8 | 6.59 | 1.20 | Spheroid |
Proteus | 436 × 416 × 402 | 5.0 | 1.3 | Irregular |
Mimas | 414.8 × 394.4 × 381.4 | 3.84 | 1.17 | Spheroid |
511 Davida | 326.1 | 3.6 | 2.0 | Irregular |
704 Interamnia | 316.6 | 3.3 | 2.0? | Irregular |
Nereid | 340 | 3.1 | ? | Irregular |
3 Juno | 290 × 240 × 190 | 3.0 | 3.4 | Irregular |
Plainly, there is no clear mass or size boundary dividing those objects in the Solar System which could be considered "spheroids" and those which are obviously irregular. The irregular objects Pallas, Hygeia and Proteus are all larger than regular objects, such as Miranda and Mimas. Also, as demonstrated by the dimensions listed in the table, the term "spheroid" is, in any case, fairly loose. Vesta, by the above formulation, could be considered either a spheroid or irregular. (see image)
The new diagram listing the changing numbers of planets is quite nice, but it does contradict the article slightly. Galileo considered his four moons "planets", though I don't know yet whether this term was widely used for them, or for how long. Until we sort this out it might be a good idea to take the diagram down for now. I'll place it here until I can get some better information.
Serendipodous 09:30, 22 February 2007 (UTC)
The picture comparing the sizes of Pluto with the Earth, the Moon and other KBOs suggests a false qualitative difference between Earth and the other objects. It is important to counter this with the observation that planets come in a huge range of sizes. The differences between Earth and Jupiter are much greater then the differences between Earth and Pluto, and that is important to deciding what a planet is. Algr 04:29, 15 July 2006 (UTC)
Serendipodous 07:43, 15 July 2006 (UTC)
Thank you! I believe this is the first time I have seen such a statement in print, and I feel vindicated. I definitely agree (disclaimer: I'm not an astronomer). When I was about 8 years old I got interested in astronomy. It seemed obvious to me from the descriptions of Jupiter and Saturn that they were unignited stars (in spite of the presence of significant amounts of methane). I've kept this opinion through the intervening 55 years, in spite of increases in my knowledge about these planets. And I would be very much surprised indeed to learn that either planet had a rocky or metallic core.
In these cases, at least, I think it is clear that an object can be viewed (and called) both a planet and star at the same time. David spector ( talk) 16:18, 6 May 2009 (UTC)
I think that, since the IAU and many astronomers insist that planets must be in orbit around the Sun, we need to coin a new word for planet-like objects in orbit around other stars.
Either that, or we should stop being so provincial and drop the requirement that a planet must orbit the Sun. We should refer to the Sun's planets as "the Sun's planets" instead of "the planets".
If we choose neither of these alternatives, as is currently the case with many astronomers, then we are forced to discuss extrasolar planets as "planets" (in quotes), since they do not fit the definition of a planet. This is unnecessarily awkward, and can only become more awkward over time as the resolution of imaging of extrasolar planets improves and the possibility of travel to them from Earth increases away from zero. David spector ( talk) 16:30, 6 May 2009 (UTC)
I really do appreciate your plaudits and enthusiasm, however, I must stress that Wikipedia is not an internet discussion forum. The talk page is really more for discussing how to improve the article. If you're interested in discussing astronomy, I can recommend the Bad Astronomy/Universe Today forum, which is frequented by many astronomers. Serendi pod ous 16:39, 6 May 2009 (UTC)
I appreciate that this is not an astronomical forum, but this article uses contradictory terms (a planet must orbit the sun but an extrasolar planet is presumably something orbiting some other star). In the absence of a defined term, the article uses a previously defined term to describe something that has been excluded by that definition. To my mind, totally unacceptable for an encyclopaedia. To use an analogy, it is akin to saying that an antipodean dog is not a dog. The problem is exacerbated because the article itself is about the definition of a planet. If this is considered the pinnacle of Wikipedia, then I am disappointed. Malchemist ( talk) 07:27, 31 July 2011 (UTC)
Under the section "Sattelites": "When Copernicus placed the Earth among the planets, he also placed the Moon in orbit around the Earth, making the Moon the first natural satellite to be discovered." "Discovered" is possibly a misplaced term here, since we're talking about an object that has arguably been observed by many lifeforms in detail over its history. I like the term "identified" better, but I wanted to run it past the talk page here. Stotan ( talk) 03:20, 7 May 2009 (UTC)
Moved discussion to talk page as per WP:NOTFORUM
Fair enough, but there is a genuinely relevant point here. The concept of "discovery" is simply not defined. Therefore infoboxes giving dates &c violate NPOV by giving special prominence to 1 POV. This applies to a lot of other stuff in infoboxes too. Peter jackson ( talk) 11:06, 5 June 2009 (UTC)
Hi,
Helping to translate the french version of this article, it appears that the quotation from Alexander von Humboldt which supposed to be in Cosmos couldn't be found in the given link. Any information on this ( pages, traductor, edition) would be appreciated.
TIA.@+ --
90.8.76.43 (
talk)
13:17, 18 May 2009 (UTC)
It's there. Unfortunately I can't provide a direct link to the paragraph because Wiki can't handle the URL and won't accept tinyurls. When you click onto the book's hyperlink, just type "unwandering orbs" into the "search this book" engine. It will say it can't find it, but then just click "search all volumes" and there it is, in that same book. Serendi pod ous 15:13, 18 May 2009 (UTC)
What does "larger by a factor of 0.33" mean? Sounds like smaller to me. Peter jackson ( talk) 10:44, 15 July 2009 (UTC)
Do Extrasolar planets (planets in other solar systems) fit in with the same definition as planets in our solar system, except "orbits the Sun" becomes "orbits a sun"? Jezzamon ( talk) 05:37, 27 August 2009 (UTC)
The sources seem to cover 2006 to 2008 with a few earlier dated sources for earlier philosophizing around language and term creation. Is the debate dead, or is it just that the wikipedians have gotten enough of a hot topic? Those of you who are professionals might know, AFAIK amateurs generally just accept the definitions that professionals claim. ... said: Rursus ( mbork³) 08:44, 2 October 2009 (UTC)
Discussion of the debate should include mention of the Great Planet Debate, organized by professional astronomers who reject the IAU definition, held at the Johns Hopkins University Applied Physics Lab in August 2008. Audio transcripts are available here: http://gpd.jhuapl.edu
This two-and-a-half day conference addressed not just Pluto and dwarf planets but also borderline objects such as protoplants Vesta and Pallas, exoplanets, brown dwarfs and the boundary between stars and the upper limit of planets, and teaching the controversy. Stern, Levison, and many other professional astronomers took part in panel discussions on these issues. It is noteworthy that Stern continues to refer to Pluto as a planet in his regular New Horizons update and that he and many planetary scientists have decided to simply ignore the IAU entirely. In talking about the discovery of Pluto's fourth moon, Stern said, "I believe that most planetary scientists know it's a planet, and we don't need the IAU to tell us it is": http://www.time.com/time/health/article/0,8599,2084606,00.html There is some thought that planetary scientists might formally break with the IAU and start their own professional organization. — Preceding unsigned comment added by Laurele ( talk • contribs) 21:53, 31 July 2011 (UTC)
Does the astronomical community have a formal definition for two planets orbiting a common center of mass like the Earth or moon, but of equal size? e.g. Two earth sized planets. The example of Pluto and charon is an example, although they are now called dwarf planets —Preceding unsigned comment added by 98.219.220.143 ( talk) 17:34, 16 May 2010 (UTC)
The section makes it sound like Sykes said the bit about Pluto being a potential planet in a different orbit, but that isn't in the reference, and we shouldn't be implying that he did. Sykes also didn't say the bit about Mars "therefore be surrounded by objects of similar mass", which is just wrong anyway (it would be surrounded, but the objects don't have to be of similar mass). Whether or not the isolated Pluto would be a planet depends on the definition "clearing..."; for example, a definition based on the Stern-Levison λ might still exclude it if the definition (like the IAU's handwaving) says that the object must clear the region, not just that the object currently inhabits in a clear region (hello Sedna!). However, I suspect we could find some reference for that argument. Finally, I don't think "ambiguous" is the right word here: with a reasonable definition, there's nothing ambiguous about whether an object is a planet or not. I left it in the first instance, but removed it from the Sykes paraphrase since that's not the expression used in the reference. Tbayboy ( talk) 00:08, 4 January 2011 (UTC)
Since editing is closed, could the first paragraphs be changed to say "pluto and transneptunian objects" rather than pluto and other transneptunian objects, since pluto isn't clearly transneptunian. —Preceding unsigned comment added by 69.180.134.188 ( talk) 05:34, 5 April 2011 (UTC)
This section is incorrect: per the IAU press release, the H=+1 criterion is not about "classifying" the object, but only about naming it, and there is no "demand" that an object meet this criterion to be named as a plutoid. This is explained well in the main article. Brown's objection (in his blog) is based on his own mis-reading, which is pointed out in one of the comments on the referenced blog page. I thought about fixing the first sentence, but then it becomes clear that this is not really a controversy but a misunderstanding, and the blog comment suggests it may have been cleared up (I didn't see anything more about it by Brown one way or the other, so can't say for sure). The whole section is then reduced to insignificance, so I took the bold to heart and nuked it. If it's to be revived, then it should be fixed to indicate what the IAU actually said, in addition to the misunderstanding that lead to the controversy. Tbayboy ( talk) 18:42, 9 April 2011 (UTC)
The language of the first two paragraphs is torturous. I'd rewrite it if editing was allowed, like this: (absolute minimum to stop my eyes bleeding when I read it)
Since the word was coined by the ancient Greeks, the definition of planet has included many things now regarded as distinct, often simultaneously. In the past the use of the term was never strict and its meaning has altered to include or exclude a variety of different objects, from the Sun and the Moon to satellites and asteroids.
By the end of the 19th century, the word planet had, without being formally defined, come to cover a smaller range of objects. It only applied to objects in the Solar System; a number small enough that any differences could be dealt with on an individual basis. After 1992 however, astronomers began to discover many additional objects beyond the orbit of Neptune, as well as hundreds of objects orbiting other stars. These discoveries not only increased the number of potential planets, but also expanded their variety. Some were nearly large enough to be stars, while others were smaller than Earth's moon. These discoveries challenged long-perceived notions of what a planet could be. — Preceding unsigned comment added by 125.237.82.60 ( talk) 10:11, 31 July 2011 (UTC)
I request the author to include Aryabhata's works and inferences to the list of astronomers (Planets in antiquity section). For more information, please see Aryabhata
Thank you,
Funkfan 08:04, 3 August 2011 (UTC)Asatya82 — Preceding
unsigned comment added by
Asatya82 (
talk •
contribs)
Is the reason that there was no improved IAU definition of planets that they wanted to pass such a decision with a large majority, but couldn't come to an agreement yet? I hope it's not that they think the current definitions are OK, because they're clearly not. For example the definition of extrasolar planet states the lower mass limit for an object to be an extrasolar planet is the same as in the Solar System... but there was no such limit given. Neither for dwarf planets nor for regular planets. There would have been no harm done if the upper limit for extrasolar planets was also applied to the Solar System, but that wasn't done either. It's like they're hiding everything behind smoke and mirrors and make up the results as they go.
It would be relatively easy to come up with criteria that could decide if a newly discovered body is a planet or not. But they didn't do it. Why? What for example is wrong with the following?
1. A planetary mass object is an object with a mass between the agreed mass limit needed for hydrostatic equilibrium (5×1020kg) and the agreed mass limit needed for deuterium fusion (2.5×1028kg). (Both limits might be set lower since the first would exclude Pallas and Vesta which are remaining protoplanets and the second doesn't take into account that objects with high metallicity could allow deuterium fusion at a lower mass)
2. A planet is a planetary mass object on an orbit around at least one star that also has the capability of clearing its orbit (per Stern-Levison criteria. The difference is you only need to know mass and orbital period of the object (and the star of course), whereas with Soter's criteria you'd need to know everything about the system).
3. A dwarf planet (I prefer mesoplanet) is a planetary mass object on an orbit around at least one star that doesn't fulfill the Stern-Levison criteria.
More definitions could be added to account for other types of planetary mass objects. I prefer "planetar" for those that don't orbit any star - regardless if they were formed by themselves or in a system of which they were later ejected. Also, I'd like "moon" to mean a planetary mass object that orbits a planet (since the prototype object Luna is just that) - smaller bodies would just keep being "satellites". (If you don't like to have 60 planets of which most are small, why would you allow 60 moons of which most are tiny?)
Any ideas why the IAU doesn't come up with something like that? Ambi Valent ( talk) 00:25, 19 January 2013 (UTC)
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