Talk:Celestial mechanics

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Merging[edit]

Should this page be merged with Astrodynamics? [[User:Sverdrup|Sverdrup❞]] 10:06, 12 Sep 2004 (UTC)

Probably; the other celestial Mechanics page is just a older copy of it. --Ben Standeven

Reading the rules of the Wiki, Celestial mechanics is the preferred title, (as opposed to Celestial Mechanics) using the lowercase name of all but the first word in the title. The subjects of Celestial mechancis and Astrodynamcs are clearly separated: the former is the science; the latter engineering. The former, objects in free flight: gravity. The latter, the addition of non-gravitational forces such as drag and propulsion. -- Marty McGowan Nov 26, 2004.

Category consensus[edit]

The categorization shows that astrodynamics is a sub-cat of celestial mechanics; astrodynamics uses the principles of celestial mechanics, as its article states. This suggests that the notice be taken down. Ancheta Wis 09:56, 20 Apr 2005 (UTC)

I absolutely agree that the notice should be taken down, for reasons already mentioned (propelled vs unpropelled flight, engineering vs science) and others. Celestial mechanics is a highly mathematical subject, which includes questions such as: (1) is the solar system stable? (2) Are other planetary systems stable? (3) How do star clusters evolve (they cast out a few members and contract, but the details are important)? (4) If you have a binary system and a new member enters, can it be captured without ejecting one of the existing ones? (I think the answer is "no"). (5) under what circumstances will one find limited chaotic motion or unlimited chaotic motion in a multibody system? All this needs to be added or linked in here and would be a bore to engineers. Pdn 19:36, 24 Apr 2005 (UTC)

The notice should most definitely be removed. Celestial mechanics and astrodynamics are two distinct subjects, the one science, as has been said, the other engineering (as in spaceflight, for example). Having said, that, this page is not a good entry for Celestial mechanics. It comes at the subject too much from the point of view of astrodynamics. It's not good. Eilthireach 20:56, 19 May 2005 (UTC)

I agree entirely. This article is very poor, and there's too much spacecraft stuff in it which should be at astrodynamics. Also, is it really necessary for both articles to duplicate material on Kepler's equation? -- 80.168.226.10 15:27, 20 May 2005 (UTC)
  1. Hohmann transfer orbit
  2. Gemini 11 flight
  3. suborbital flights

belong in Astrodynamics, not here Pdn 01:39, 21 May 2005 (UTC)

I agree that those three belong in astrodynamics Dpu2002 15:02, 16 June 2006 (UTC)

Open Problems[edit]

Some unidentified person has put in a section on "open problems" (if you hit her/his talk page it is a group page). I thought that it was proven a long time ago that you can't get an analytic solution for even the three body problem (except very restricted cases like Lagrange points). So I suggest this be deleted or rephrased. Anyway, it does not say "analytic" so it is ambiguous, too. Computer solutions exist for very many orbits but may fail long-term, although recently "symplectic methods" seem to handle that (e.g. for the life of the solar system so far). Pdn 01:34, 15 Jun 2005 (UTC)

Expansion[edit]

Um, I'm a bit confused about the talk above regarding "taking down the notice." I'm assuming that the discussion is concerning a merge/catagory notice, and not the expansion notice that was at the top of this page. I personally think the article should be expanded -- right now it's mostly history. With that, I'm moving the expansion request to the article itself. MFago 03:26, 18 March 2006 (UTC)

I just compounded the problem by tidying up the history section. I agree that there is a need for someone who really knows modern celestial mechanics to provide a good readable introduction to its fundamental concepts, principles, and methods. The examples of problems section is too rapid a jump without a good grounding in the nature of the discipline. --SteveMcCluskey 18:57, 22 January 2007 (UTC)

Circular Orbit Assumption[edit]

The section in the article describing the circular orbit assumption seems misleading. When I read it, I get the idea that circular orbits are assumed very often, when this is far from the case. Maybe its just me sucking at reading today, does anyone else think that? Dpu2002 15:01, 16 June 2006 (UTC)

Neat little law:[edit]

This is something about orbits I read a little while back, that might be appropriate in this article:

In order to slow down, you speed up; to speed up, you slow down.

Slowing down puts you into a lower orbit, which is faster in relation to a point on the surface of the body you are orbiting around. Speeding up puts you into a higher orbit, which is slower in relation to the aforementioned point.

Can anyone think of a place to put this?

Phædrus 00:05, 20 March 2007 (UTC)

Split off history?[edit]

Any sentiment here for splitting off the history section to a separate article? It seems out of balance and bloated to me, yet at the same time cursory and inadequate in its treatment of the history. Wwheaton (talk) 21:16, 4 October 2009 (UTC)

[From Terry0051] I'd suggest that the genuine history is an essential part of this subject and should not be split off. The parts of the current history section that deal with the genuine history are cursory and inadequate I agree. But there are other parts currently present that look anachronistic and unconnected. Leibniz, as the article says, was the first to talk of dynamics in this connection (while Newton preferred 'rational mechanics'), and the attempt further down to father dynamics off on to Thomas Aquinas or Averroes looks like unsupported and mangled anachronism and deserves to be removed. Maybe there's a case for including some of Newton's 17th-century predecessors for their contributions of elements that were developed into parts of his systematic and rational mechanics, but otherwise I suggest this history really does start with Newtonian mechanics. Terry0051 (talk) 01:09, 5 October 2009 (UTC)
I think I still favor a separate article on the history, for which the current history section could be a start-class seed. Then that article could be expanded without further bloating this article, which really should summarize the content of the subject.
Our real problem here (I think) is that this article hardly presents the subject at all, and needs to be filled out in some more substantive way. The material to do a good job on that already exists in a number of other more specialized articles in Wikipedia. Then this article could have sections giving a substantial overview summarizing the core concepts and methods, linked to the more specialized articles. A shorter history section would then fit in well here. Wwheaton (talk) 07:30, 13 February 2011 (UTC)
The term Celestial mechanics is well-defined in the introduction:
"The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data."
The history section, however, ranges into a wide range of other fields of astronomy from antiquity through the renaissance where either ephemerides were computed without any physical presuppositions (consider the Ptolemaic and Copernican geometrical models) or the physical natures of celestial bodies were discussed, without using them to "produce ephemeris data." The historical topics before Kepler are already well discussed in Wikipedia in a range of other articles on different aspects of the history of astronomy or cosmology. Perhaps most relevant to this article is the article on Dynamics of the celestial spheres. I suggest deleting the entire history section from Ancient Greece to Late Middle Ages, possibly with a reference to other appropriate articles. SteveMcCluskey (talk) 20:36, 12 June 2013 (UTC)
Absent comments, I've Boldly revised the history section, removing the material before Kepler. Further discussion is welcome. SteveMcCluskey (talk) 18:01, 15 June 2013 (UTC)

"Emits"?[edit]

I have temporarily reverted an edit by User:William M. Connolley, concerning the usage of the verb "emit". I checked Wiktionary, where it is defined as "To send out or give off", which reflection of light would seem to satisfy, especially at the atomic level. While the modern usage in physics does favor reflection as being distinct from emission (our article List of light sources, to which Light emission redirects, does not mention reflection), in the context of medieval understanding this was probably a hazy point, possibly confused in the translation from Arabic. In any case, the paragraph needs to be reworked a bit (which I cannot do immediately) before changing it, as emits is used more than once. Wwheaton (talk) 03:13, 13 February 2011 (UTC)

Looking at it now again, we cannot change "emit" without mangling the quotations. The translator might better have chosen a different word, but our modern usage in physics would perhaps have been lost on Ibn al-Haytham, who had no way of knowing if the light was reflection or florescence, or what — just that it was sent out or given off (in all directions) wherever sunlight struck the spherical Moon. Another possibility would be to truncate the quotation before emit & emitted appear, and replace them by "diffusely reflect" or some such, but that carries his meaning forward to our era in a way that seems dubious. Or just substitute "send out or give off" before the truncated quotation. Personally, I think it best just to leave it as-is, as the central celestial mechanical point seems clear enough. Wwheaton (talk) 07:10, 13 February 2011 (UTC)

No mention of Descartes[edit]

Someone (less lazy than I) should add a section on Descartes's vortices. According to the Isaac Newton article, Descartes's theories were preferred by many to Newton's for decades. The Stanford Encyclopedia of Philosophy has an article that describes these vortices: <http://plato.stanford.edu/entries/descartes-physics/>. — Preceding unsigned comment added by Iain.dalton (talkcontribs) 01:45, 2 August 2012 (UTC)

Descartes' vortex model did not develop the kind of quantitative predictions of planetary motions that characterize celestial mechanics. In fact Newton discussed the failure of Vortex motion to account for Kepler's third law in his Principia, at the concluding Scholium to Proposition LII, Theorem XL (Motte and Cajori transoation, p. 394):
"...certainly neither the 3/2th power, nor any other certain and determinate power, can obtain in them [i.e., in vortices]. Let philosophers then see how that phenomenon of the 3/2th power can be accounted for by vortices."
Unless we want to expand the concept of celestial mechanics to general discussions of celestial physics, Descartes doesn't fit here. SteveMcCluskey (talk) 19:47, 15 June 2013 (UTC)

A section for Laplace[edit]

Isaac Newton says: a century later, Pierre-Simon Laplace's work "Celestial Mechanics" had a natural explanation for why the planet orbits don't require periodic divine intervention. - that sounds like he had some significant contribution to the field. If that's the case, maybe he deserves a section in this article? —  Ark25  (talk) 18:10, 1 July 2014 (UTC)