Talk:Definition of planet/Archive 4

message: The current article contains a paragraph that describes how any moon-planet system may be considered a double-planet.  The paragraph goes on to say that "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."
I disagree with the statement that the mass of the moon does not change the required distance.  I also disagree with the statement that as the planet's mass decreases, the required distance to the moon increases.
The period of orbit of one body about another depends upon the mass of both bodies, as this is what determines the gravitational force between the two bodies.  However, as a first approximation, the mass of the smaller body is usually considered to be small when compared to the mass of the larger, and hence the orbital period calculation, in this instance, can be said to depend only on the mass of the larger body.  This is usually the case in Earth's solar system, although since the article is attempting to be general and apply to any system of orbiting bodies, the approximation may not hold true in all circumstances.
On the second point, even if we assume that the mass of the moon is small, then as the mass of the planet decreases, the gravitational force between it and the moon will also decrease.  Hence, the period of the moon at that orbital distance will lengthen.  Therefore, the moon could orbit at a closer orbital distance and still have an orbital speed slower than the planet's speed around the star.  Therefore, the required distance between the moon and planet decreases (the article as it is written says "increases").
There is no reference for the statement in the article but the article has apparently been peer reviewed so I assume someone has checked this out, and I am interested is reading what that person(s) has to write, as I am open to a complete discussion of the dyanamics of orbiting bodies and may learn something on my part.  I did not make any changes to the main article for the same reason.
D. Clippinger
:I'd be interested to see this issue resolved. I've been meaning to source that paragraph for a long time (for the record: I didn't write it) but lack the knowledge of Newtonian dynamics to do so. Serendipodous 19:08, 16 August 2006 (UTC)
replies: text: Drat, this means that I have to break out my physics book and figure it out. Could someone get me a reference of who added that particular change while I'm doing the math? McKay 20:31, 16 August 2006 (UTC)
replies: text: His name was Tompw. Serendipodous 08:38, 17 August 2006 (UTC)
thread_title:  Orbital period of the moon and the planet 

message: There’s a preprint by Michael E. Brown and Basri, Planetesimals to Brown Dwarfs: What is a Planet?, . But you’ve probably seen this...Eurocommuter 17:55, 22 August 2006 (UTC)
thread_title:  Brown's POV. 

message: There seems to be a new proposal for the definition of a planet that the IAU is favoring now.  See Talk:2006_redefinition_of_planet#Latest_Draft.  In an nutshell, this proposal adopts the criteria that a planet be by far the biggest object in its "orbital neighborhood".  In fact, one of the articles linked to in that section says that August 22 is now "the day we lost Pluto". --EMS | Talk 03:45, 23 August 2006 (UTC)
replies: text: Yes, planets have largely cleared out their orbits (as Jupiter has), but the main issue is whether the object "dominates" its region (as Jupiter does--the Trojans only orbit where they do because of Jupiter). Ceres does not dominate in this way; you could take it out of the asteroid belt and the belt would continue to exist in much the same form as it does now. As for "world" I think this is similar to the term "continent" in geology: permanently undefined. I.e. it's a lay term, not a scientific term. --Aelffin 15:31, 24 August 2006 (UTC)
replies: text: Look up trojan asteroids.  Jupiter has not cleared its orbit as well as even Earth had.  Pluto and Jupiter seem to be in more populated regions than Earth and Mercury.  The definition is very fluid and arbitrary, IMO.  But that does not affect this article.  They've decided it.  And I guess that's that until someone wakes up.  Hopquick 23:33, 24 August 2006 (UTC)
replies: text: Both Jupiter and Earth have cleared their orbits in the sense that the IAU means. Read Clearing the neighborhood.--Aelffin 12:48, 29 August 2006 (UTC)
thread_title:  New IAU proposal 

message: After my short-lived edit, I went through the archived discussions and saw numerous comments where people assert that Vesta is spheroidal, but I did not find much external reference. Several say that Vesta really is an oblate spheroid if you ignore the big crater. But isn't that exactly the point? Vesta did not have sufficient gravity to collapse back into a spheroid. That sounds to me like it doesn't have hydrostatic equilibrium.
Google Scholar returns mixed inconclusive results, AFAICT. The abstract of the Icarus article (also mentioned in the archives) gives a statement that could be interpreted in either direction. Frankie 17:10, 24 August 2006 (UTC)
thread_title: Vesta

message: Are the paragraphs where moons whose orbits of their planet does not overlap when viewed from above could be considered part of a double planet system OR, or is it just me?  The only cited source does show that the moon's orbit around the Earth is a wave rather than a spiral, but it makes no mention of this making it considered to be a double planet and actually says several times that the Moon orbits the Earth. Page 2 of the cite even says it orbits Earth once every 27.3 days. The definition of a satellite also contradicts the inclusion of these moons as being partners in a double planet system.--Bobblehead 20:10, 25 August 2006 (UTC)
replies: text: The section also says the Moon orbits the Earth. But the Moon also orbits the Sun directly. Yes, the official definition should be mentioned as contradicting this, but that doesn't lessen its value as a potential ambiguity in the agreed definition. Just edited the section. Serendipodous 20:55, 25 August 2006 (UTC)
replies: text: This may be true, but unless you can find a source that supports this claim it is still OR. Take a look at the What is excluded? section.  The statement seems to meet all but two of the list and as such probably should not be included, unless a reputable source saying moons that meet that criteria can be considered a double planet system, of course.--Bobblehead 21:14, 25 August 2006 (UTC)
replies: text: How about this? EDIT: Couldn't wait. Swapped it out. Serendipodous 21:22, 25 August 2006 (UTC)
replies: text: While I do admit that Isaac Asimov is a smart guy (I've actually read his essay books), I do find it amusing that he quoted him. Heh. That being said, even if it is a commentary, the article you provided seems to meet the Reliable Source criteria for stating that the Earth and Moon relationship might be a double planet relationship.  It doesn't, however, support the remainder of the section regarding how the lack of a spiral orbit path around the sun in relation to the primary bodies orbit means any other satellites may cause it to be considered a double planet. The article seems to be saying we just don't know enough about how a moon is formed to know the origin of the moon. However, I'm off camping for the rest of the weekend. Thanks for working with me. --Bobblehead 22:08, 25 August 2006 (UTC)

text: If you go up top, you'll see that that subequent paragraph is already under scrutiny. Serendipodous 14:52, 27 August 2006 (UTC)
thread_title:  Double planet section 

message: The section "IAU debates" doesn't distinguish clearly between the final draft  and the approved decision. There is no mention of the decision in text at all. Andres 13:23, 27 August 2006 (UTC)
replies: text: What approved decision? Serendipodous 13:43, 27 August 2006 (UTC)
replies: text:  What I mean is that the phrase "final draft" is used but there is no mention that the draft was passed and approved by the vote. Andres 14:41, 27 August 2006 (UTC)
thread_title: IAU decision

message: Check out the link.  Is there anything needed to be said about the strengthening rejection of the 2006 definition?
http://www.ipetitions .com/petition/planetprotest/   Hopquick 17:58, 2 September 2006 (UTC)
replies: text: While I agree with the principle of an open, grassroots debate leading to a consensus, and think that was how the definition should have been arrived at in the first place, I feel the need to point out that there are fewer names on that protest than actually voted for the final proposal at the IAU. Serendipodous 18:09, 2 September 2006 (UTC)

text: Agreed. This is just an attention-getting device. Not related to real science. Don't  give them the satisfaction of being mentioned in the Free Encylcopedia.--Planetary 18:33, 2 September 2006 (UTC)
replies: text: It's the Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS) that is upset with the definition.  Not just a few... Your quick dismissal might betray a bit of bias. ^_^ http://www.space.com/scienceastronomy/060831_planet_definition.html Hopquick 04:27, 3 September 2006 (UTC)
replies: text: After reading the link, I don't really see what it is you're talking about. Sure the DPS of the AAS doesn't like the definition according to the article, but the AAS website says nothing, except referencing the IAU proceedings, the DPS site hasn't been updated since May. While I think they may have made a statement, all they did was request for clarification, not protest the decision, the article says that the DPS even "recognizes the authority of the IAU to render a decision." The group of 300 people who refuse to use the new definition is small, though probably "notable") compared to the people who actually voted in the affirmative in the IAU decision. The IAU even claims to fix these unclarities in 2009. If we find 90377 Sedna is mostly by itself before 2009, then we might be in a little bit of trouble, but we'd have to wait for 2009 anyway, because the IAU is the recognized governing body (with recognized authority that is virtually universal) with regards to astronomical nomenclature. So my vote is to recognize that there is some protest (the space.com article is notable), but it doesn't have to be much. I think the current article is perfectly satisfactory in this regard. McKay 05:46, 3 September 2006 (UTC)

text: I can't see any bias here. In the article the statement of one division of the astronomical society of one country is reported. And they even *supported* the decision. That the support was "lukewarm" is merely the interpretation of the author who by himself is obviously not an unbiased one. And since the statement was not voted upon by the members it's even much less a statement of *the* DPS than the IAU decisions was the decision of *the* IAU. 84.165.159.183 13:51, 3 September 2006 (UTC)
replies: text: My first link was the more relevant one to the discussion.  But there seems to be consensus against the inclusion of this. (That's what the talk page is for, is it not?)Hopquick 15:34, 4 September 2006 (UTC)
replies: text: Heh, I decided to look at what else ipetitions.com has up, and the two most recent changes (Bring back SG-1, and bring back a shopping center in Houston), each have over 20,000 signatures. Even .com/petition/Ice_MUG/signatures.html computer users in Iceland can get over 300 signatures on a petition. And that has very limited scope. It seems as if the astronomers' petition is rather minor. McKay 15:48, 4 September 2006 (UTC)

text: NPR's Science Friday is reporting on the protest.  Not just anyone can sign this petition. - it is 300 planetary scientists and astronomers compared to only 428 who were involved in the IAU decision in the first place. And this was in only five days.  It certainly belongs in the article.  Algr 17:41, 14 September 2006 (UTC)
replies: text: It is mentioned in this article, briefly. Since this is a broader, more historical perspective, if that protest belongs anywhere, it belongs in the 2006 redefinition of planet article.Serendipodous 17:48, 14 September 2006 (UTC)
thread_title:  Protest 

message: The article says that only some 400+ astronomers voted in the vote on the definition. But this report of the voting (third post) gives different figures, and says that there were a lot of abstentions. I think we can only refer to reports of the numbers voting, as I have seen no official source, rather than make a bald statement of fact. --Cuddlyopedia 16:25, 18 September 2006 (UTC)
thread_title: IAU voting numbers

message: 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)
replies: text: 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)
thread_title:  Definitions of planets in fiction 

message: 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)
replies: text: Indeed, Pluto has also recently been assigned a minor planet designation - 134340. --Neo 12:11, 12 February 2007 (UTC)
thread_title:  Minor inaccuracy removed 

message: 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)
thread_title: Recent addition

message: The article discusses at length whether objects are spherical and therefore dwarf planet candidates. But sphericity is not a criteria for that status. The criteria is "has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium", which is then paraphrased as 'nearly round'. Objects can be spherical for reasons other than their mass. And objects can be in gravitational hydrostatic equilibrium and not be spherical, because of high rotation etc. I think the title of this section, and the emphasis of the content, should be changed to reflect this. Sphericity is a good first sign though, so most of the content can be kept. --Cuddlyopedia 16:25, 18 September 2006 (UTC)
thread_title: Sphericity