Astronomy: Moon / Solar System Redirect‑class Low‑importance | ||||||||||||||||
|
To-do list for User:Rich Farmbrough/temp331: To-do list is empty: remove {{To do}} tag or click on edit to add an item. |
If things like "synchronous rotation" are to be kept, then it makes sense to rename this article to "The Moon (motion)" from the current "The Moon (orbit)". mdf 15:03, 11 July 2006 (UTC)
I had an argument with a friend who said that the distance between the earth and the moon was increasing. From what I know about physics, this is impossible. Orbital energy must be lost due to tides etc. However, he argued so convincingly that I came here to know for sure. If he is correct, I think it deserves a section in the article, if he is wrong, the decay rate of the orbit would be an interesting factoid to add to this article.
: Roguebfl 11:05, 25 August 2006 (UTC)Predictions suggest that the range will increase until the Earth and Moon become double synchronised, that is, both are tidally locked to one another. (So the Earth's day length would match the Moon's future orbital period of about 47 days, and the Earth-Moon distance would be about 550000km, compared to today's figure of 400000km). This won't occur for something like 50 billion years, by which point the Sun will be a white dwarf and will have passed through a red giant stage, which may result in the destruction of the Earth. [1]
In the heading Inclination of the rotation axis, this article explains the axial tilt as 6.69° to ecliptic (my emphasis).
However, in the table lower down Other properties of the Moon's orbit Mean inclination of lunar equator to ecliptic is listed at 1° 32' Roo60 12:50, 15 July 2006 (UTC)this is really confusing for some people
Proposal: Merge Earth and Moon with either The Moon's orbit or Tidal acceleration.
The result of the debate was merge with tidal acceleration. — Lunokhod 21:12, 4 December 2006 (UTC)
It has been suggested that Earth and Moon be merged with either The Moon's orbit or Tidal acceleration.
FOR: I am for the move for the following reasons
I think that the some portion of this material could be placed in The Moon's orbit, but that Tidal acceleration is where the bulk of it should go. Lunokhod 18:46, 22 November 2006 (UTC)
ALTERNATIVE: The Earth and Moon page mainly deals with tidal evolution of the orbit. That topic has been treated at length on a separate page: Tidal acceleration. So I propose to merge Earth and Moon with that page instead. Do change the link on this page though. Tom Peters 11:47, 23 November 2006 (UTC)
Recently the statement that Earth+Moon form a double planet has been reversed. That apparently has been done on the grounds that the COM lies within the Earth. That is only one possible criterium. IMNSHO it also is a poor one: if the Moon were twice as small but four times more distant, the COM would lie outside of the Earth, and the smaller Moon would be part of a double planet anyway? Asimov's proposal, based on the fact that the Moon orbits the Sun rather than the Earth (also looking at the actual shape of its orbit in space) makes more sense. Anyway, with even the concept of "planet" in confusion, I don't believe we have a solid base to securely classify E&M as a double planet or not. Tom Peters 10:45, 4 December 2006 (UTC)
Asimov's proposal of considering the Earth-Moon system a double-planet system is based, yes, on Moon's orbit around the Sun, Moon's size and mass in comparison to Earth's (only the Pluto-Charon system come close in proportions - that one fully recognised as a double-planet) and also (I believe this is the most important point) the "tug of war" (Asimov's name): Sun's gravitational pull on Earth is stronger than Earth's. This is true only for Moon among all other big satellites in Solar System (some of the outer, tyniest moons of Jupiter and Saturn also have this property), false even for Charon. It also makes me doubt that, if Sun would dissappear suddenly, Moon's orbit around Earth would continue as if nothing had happened. Since Sun's gravitational pull on the Moon is stronger than Earth's, I'd expect Moon decaying into a lower orbit in case the Sun dissappears. Can anyone support the claim that "nothing would happen" with some calculations, or providing an animation using "Gravity" or any other simulation program? Thanks —Preceding unsigned comment added by 148.244.69.177 ( talk) 22:54, 16 October 2007 (UTC)
Proposal: Rename The Moon's orbit to Orbit of the Moon.
The result of the debate was move. — Lunokhod 10:50, 7 December 2006 (UTC)
FOR I am for the proposed rename/move because (1) it is not wikipedia policy to have pages started with the word "the", and (2) when listing this page in an alphabetic list of see alsos, this topic falls under "the" (hence the reason for the naming policy). Lunokhod 21:26, 4 December 2006 (UTC)
Makes sense. I agree. Tom Peters 23:23, 4 December 2006 (UTC)
You know, I just came over here to propose that idea myself. 100% agree. The Moon's Geology, The Moon's Exploration etc. would look just as bad. Fine if we're writing in Swedish (Indiens flagga for Flag of India for example), but not English. Mithridates 02:10, 7 December 2006 (UTC)
The perigee listed in the article may be good for an "average" month but the moon has been known to come as close as 356,300 km. Someone should find a better source. Sagittarian Milky Way 05:00, 23 March 2007 (UTC)
356337.064 -2338 Nov 09 03:22:22 356349.827 -2683 Nov 13 02:33:02 356352.945 -1055 Nov 13 21:40:37 356354.171 -2665 Nov 23 13:31:54 356356.491 -0851 Dec 08 02:26:27 356356.657 -2356 Oct 28 16:22:36 356360.917 -1400 Nov 17 21:11:04 356365.136 -2320 Nov 19 14:21:41 356365.621 796 Dec 19 05:44:44 356366.204 -2869 Oct 30 08:25:51
370389.858 -0367 Nov 19 13:58:27 370390.249 -2915 Nov 20 20:59:18 370391.003 -2588 Nov 05 10:27:44 370392.976 -0256 Dec 06 21:55:54 370393.790 -2699 Oct 18 19:22:03 370394.088 90 Dec 03 02:19:14 370395.483 -2933 Nov 08 21:26:07 370397.683 -1212 Nov 16 20:04:09 370404.210 -2088 Nov 11 23:55:44 370407.525 -1650 Nov 15 01:16:01
I see from the article that the ellipse of the lunar orbit rotates counterclockwise, and that the precession of its orbital plane is clockwise. How about the orbit itself? The animation of the Moon as it cycles through its phases allows one to infer that the orbit is counterclockwise (same as the rotation of the Earth, and the Earth's orbit around the Sun) but this really should be stated explicitly both here and at Moon. -- Wfaxon 22:01, 28 July 2007 (UTC)
Someone looking for info on the "secular acceleration of the Moon" in Wikipedia will search long and hard. Perhaps it is here but searching on this familiar term yields nothing. Cutler 09:51, 24 August 2007 (UTC)
The equations which are said to be the basis of the image are not clear. In the first place the given equations of the earth's orbit would describe a circle, not an ellipse? This is easily corrected and should be shown as precisely as possible in an encyclopedia article. In the second place, the origin of the symbol " p:(synodic months+1)=14 " is not clear. If "p" is a constant(14), then how can it be an integer? Should it be more precisely the number of synodic months in a sidereal year ~12.368? And why plus one? Will the contributor of this image and these equations please clear this up? PSpace —Preceding unsigned comment added by Alexselkirk1704 ( talk • contribs)
I've searched the internet, and can only find recorded dates for one of the lunar cycles, the synodic. This is a problem due to the importance of the draconic (nodical) cycle in predicting eclipses. Someone should do some research. 68.144.80.168 ( talk) 08:00, 30 March 2008 (UTC)
According to this article, cited by a source I can't access, the Earth and the Moon will achieve spin orbit resonance in 2 billion years. This seems a remarkably short time. I've heard estimates as high as 50 billion years. Serendi pod ous 16:08, 8 June 2008 (UTC)
There are two changes under discussion with both being in the Orbit of the Moon#Path of Earth and Moon around Sun section.
(Unindent otherwise the lists below get really to read.) The distinction is made on both the convex and concave polygons and convex set articles in that they note that the observer's position is inside the shape when taking the measurements that determine if it's convex or concave.
I have two questions:
While pondering that; Here are definitions from my dictionary starting with convex. The italics are my comments.
That's it for the convex definitions. Here is concave
The point is that when words like convex and concave are used care is taken to note the observer's position, and if needed, the orientation of the subject described.
This is why I commented on the illustration caption. The caption itself fails to orient the observer and then in parentheses leads the reader, and presumed observer, to a spot where the subject would be interpreted as concave per any of the dictionary definitions. This is why I suggested that the illustration caption be changed to “From the point of view of the Sun (far left down), the Earth and Moon's path around the Sun is always concave.”
An alternative wording: "The area inside the Moon's orbit around the Sun forms a convex set. The sun is to the far left and down." Or, "Detail of the Moon plus Earth system as it orbits the Sun which would be to the far left and down. The orbit is convex when viewed from the outside (upper right corner)." Either attempt to use convex correctly seems more convoluted than identifying where both the Sun and observer are and calling the Moon's path concave.
I'll see if I can make a better image. I found the web site it was stolen from a bit ago but would need to Google that one up again. -- Marc Kupper&;;;;;;;;#124; talk 01:58, 26 March 2009 (UTC)
[From Terry0051:] I agree with all of Marc's answers to the modified questions quoted as follows (with clarifications as offered below):-
"Q1: Do you think the Moon's path around the Sun is concave when looking inward at the entire Moon/Earth/Sun system? A: No.
"Q2: Do you think the Moon's path around the Sun is concave when looking outward from the POV of the Sun? A: Yes.
"Q3: Do you think the Moon's path around the Sun is convex when looking inward at the entire Moon/Earth/Sun system? A: Yes if you you view part of the orbit and treat it as an open curve) and "sort of" if you look at the entire system as the correct term is that we what the orbit defines is a convex set and not just "convex."
"Q4: Do you think the Moon's path around the Sun is convex when looking outward from the POV of the Sun? No.
The clarifications offered are:
A: We are talking about the Moon's curved path, relative to a non-rotating solar-system-barycentric reference frame - or heliocentric reference frame. (For the present purpose it does not matter which.)
B: All of the above answers have been given from the physical POV of an observer located either near the Sun, or else at a great distance away and from somewhere on or near the solar system's invariable plane.
C: None of the above answers have been given from the physical POV of an observer located on the Moon's path itself, and in relation to the small element of that path which is close to the observer (which seems to match the 'open curve' referred to in Marc's answer 3). (A physical POV located on the path-element is the one effectively used in the online astronomical references provided.)
D: Every element of the Moon's orbital path has its own curvature and center of curvature -- regular sources on calculus and orbital dynamics provide. From the physical POV of an observer located on this curved path-element, it is concave towards its center of curvature, and convex away from its center of curvature. This corresponds with the usage of concave and convex that occurs in the astronomical references already supplied.
E: There is no reason to believe the Moon's path is precisely periodic, many reasons to believe it is not, and it seems unnecessary for present purposes to go into the long-term behavior. The local curvature of the path-element that the Moon is traversing right now is defined by the dynamics of the Moon's position right now. Also, the motion is not, in physical fact, confined precisely to a single plane. These astronomical facts, and the probable absence of any closed curve for the orbital path, also make the language of convex sets seem somewhat alien from the physical situation under discussion.
As I read the original text, its task was to convey, in brief and less-technical language, the physical fact that the center of curvature of every element of the Moon's curved orbital path (in the non-rotating reference frame of the solar-system barycenter) is always on the inward side, towards the Sun, and there is no inwards-outwards alternation as the Moon makes its progress along its path.
The purpose of making this whole point seems to have been to convey, that while intuitive thinking might indicate that the center of curvature of the Moon's path at new-moon is away from the Sun and towards the Earth, that is not in fact so.
The less-technical language omitted a number of details, such as, that the center of curvature is not precisely in the Sun-Earth-Moon plane, nor in any other single plane. That simplification seems reasonable in a brief description, because the out-of-plane deviations remain small enough to neglect for this purpose. That is, the component, in the line from Moon to Sun, of the direction vector from the Moon towards the center of curvature of the path-element that the Moon is currently traversing, always points M->S, never the other way.
But it looks as if the recent edits have uncovered a point in the simplified language used in the original article, which was unclear to the general reader: i.e. the usage and physical POV of 'convex' and 'concave' -- even though these were clear to the authors of the cited mathematical-astronomy references, and to others familiar with the calculus of orbital dynamics.
I still think it is clear that the original text, before the recent edits, was correct -- given prevailing usages of the words employed in the mathematical-astronomy field -- and is now in error. But I agree that it would be helpful if the text on this point is given brief and correct clarification. If the words chosen differ from those that are usually encountered in the astronomical refernces, it would also be helpful to let the reader know in some way what to expect as the usage in the outside world if s/he is interested enough to look up the cited astronomical references.
I suggest to Shaheenjim that he looks at the Godfray and Turner references which are online and only need one click of the mouse to reach. Terry0051 ( talk) 15:58, 26 March 2009 (UTC)
[From Terry0051]: Marc, there is a more informative definition in " Wiktionary - convex" "curved or bowed outward". This shows clearly that the current wording in the article "convex towards the Sun" is clearly wrong, it would mean 'curved or bowed outward towards the Sun'.
The way Shaheenjim has put it, "a distinction between convex/concave when looking outward from the inside, and convex/concave when looking inward" is both a confusing formulation in itself, and not the way in which the point has been formulated, whether in the references, in the article, nor by the other participants in the discussion. It would be more helpful to the discussion to use one of the clearer formulations on record.
The ostensible 'conflict' based on the use of the words 'convex' and 'concave' has already been explained as not a conflict, based on the differing physical POV relative to which the words were applied. Please look again at the Vacher reference, page 5, Fig. 2B, and the description "everywhere convex outward", and then compare that with Turner, page 119, where it is made clear in connexion with an idealized case in which the moon moves around the sun in a circle, that is an example of a path that is 'always concave to the sun'. I am sure that you can see very easily how those two statements can be made about the same curve without being in conflict.
The Turner and Godfray references are both in the mainstream astronomical literature, and it would be well if the general reader is alerted, at least in a footnote, to expect their usage, for the reason already offered. The orbit of the moon is not a closed curve and better descriptions of its curvature would probably be given in terms that include center of curvature and curvature. Terry0051 ( talk) 20:35, 26 March 2009 (UTC)
[From Terry0051] Thank you Shaheenjim for your further edit, and I agree with it as far as it goes, but it leaves the ambiguity in 'convex' unaddressed. I was about to do something almost the same, retaining the word 'convex', along with a clarifying phrase based on Marc's answer #3, plus a footnote that advises of the alternative usage in respect of the same geometry. The clarifying phrase, and the explanatory footnote, I've now put in. I believe this is securely sourced in the cited references and hope and believe it otherwise reflects common ground between parties to the current discussion. Terry0051 ( talk) 21:14, 26 March 2009 (UTC)
As the Moon orbit becomes larger, eventually the year will become exactly 12 synodic (or 13 sideric) months. Will this cause any resonance effect, like the orbit getting more excentric, or is the orbit too irregular for such resonance effects? Ambi Valent ( talk) 23:52, 30 April 2009 (UTC)
The diagram in the section "Path of Earth and Moon around Sun" only shows a small part of the orbit of the Moon relative to the Sun, in order to illustrate the "convexity" (or "concavity") point. The diagram is not apt to illustrate the direction of movement of the Moon along its orbit (and in any case, insufficient information is given to define this direction, because the diagram might equally be considered as seen from the north, or from the south). But to clarify the "convexity" point, it is important to say what is the location of the Sun relative to the portion of orbit shown in the diagram: the Sun is located below and to the left. Terry0051 ( talk) 12:33, 2 May 2009 (UTC)
Joe and Terry: The diagram of lunar orbit 'convexity/concavity' you prefer has been around for at least a hundred years, since Young's 1902 Manual of Astronomy. Considering the voluminous discussion above about whether your reverted diagram makes clear orbital direction and whether viewed from up, down, inside or out I felt that the diagram I submitted made those key points absolutely clear to the casual reader of Wikipedia. Perhaps you would care to clarify your objections to describing the orbit as a modified cycloid and why the diagram that shows this is unacceptable? Geologician ( talk) 10:16, 26 June 2009 (UTC)
[From Terry0051]Hallo Sagittarian Milky Way:-- Yes, I believe you're completely correct in your reading of the text, fwiw I agree with you that's what the author meant.
Hallo again Geologician:
-- A direct quote of an isolated sentence is out of context if it doesn't take account of the overall message, what the text as a whole is talking about. You didn't take the overall message into account, your isolated sentence was out of context.
-- (Also, there's something like assuming good faith, giving the author reasonable credit, assuming that he probably had some sense and probably wasn't trying to say a crazy thing that nobody ever believed, and choosing a sensible reading of the whole if one is available. If a reading doesn't do that, it may end up looking like a perverse reading.)
-- I agree that Young (in its original form) is a 'reliable source' under the usual conditions: but that doesn't apply to any altered version.
-- You misquote me more than once, (a) I didn't deny Young as a reiable source and (b) I didn't say that the sign of the curvature 'cannot' change, only that there are proofs here that it does not change: those proofs are in the cited articles where they show that the orbit is always concave. It doesn't appear reasonable for you to assert that there is 'no supporting evidence'. But your suggestion that Young's statements apply only to 'an individual synodic month segment' does appears to be an invention of something not present in Young or anywhere else at all.
-- Where is your reliable source for 'judicious exaggeration'? I would say that whatever may be 'judicious' exaggeration, changing the shape is not, and the onus is on an editor who wants to 'exaggerate' to find RS in support.
-- You haven't shown any reliable source for the cusps, and your diagram does not resemble any of the diagrams in the reliable sources -- please read Sagittarian Milky Way's very good description of the real characteristics or the orbit by somebody who does 'get the point': [Quote: "all that is within the power of the Moon's feeble orbital speed of it's own to do is shallow up the radius of curvature of it's still concaveness to that of a 1.5 AU orbit's (temporarily of course, no spiral) instead of the nominal 1 AU radius."] Terry0051 ( talk) 23:56, 28 June 2009 (UTC)
None of your cases represent the Moon's path. Only n=13.37 and b=a/389 do (which Turner approximates in case 3 as n=13 and b=a/400). Turner's cases 1 and 2 do not represent the Moon's orbit. I have already stated many times that other moons can have any conceivable orbital shape relative to the Sun, including hypothetical and unrealistic exaggerations of the Moon's present orbit—those that maintain 12.37 synodic months per year regardless of size even though those orbits violate the universal theory of gravity. In my "exaggerating" discussion above I stated that if the Moon's orbital radius is increased beyond b=a/169.4 (while maintaining n=13.37) it developes a bulge inward, which means it ceases to be everywhere convex outward. This only shows that Turner's model is correct because it can generate all possible orbits, including the Moon's orbit whose convex outward shape is only possible with parameters near those of the Moon's actual orbit. — Joe Kress ( talk) 03:52, 3 July 2009 (UTC)
[From Terry0051] I believe it's relevant to the improvement of the main article to give cross-references here to the following two matters (especially because of the amount of editorial efforts that have been put into this section here, and because of the length and character of the discussion):
Recent change was said to be a 'correction' from 1.023 'km/s' to 'm/s'. Mean distance from the Earth is about 385000 km (not m), mean sidereal period is 27.321661 days of 86400 secs, (385000 x 2 π )/(27.321661 x 86400) comes to about 1.024 in km/s not m/s. After a chance for anybody to point out mistakes in this , the 'correction' should be reverted. Terry0051 ( talk) 22:47, 1 December 2009 (UTC)
In Path of Earth and Moon around Sun the article says "Unlike all other moons in the solar system, the trajectory of the Moon is very similar to that of the Earth". In context, I assume this refers to the fact that the motion of the Moon as viewed from the Sun is never retrograde. This is a consequence of the fact that the Moon's orbital speed relative to the Earth is smaller than the Earth's orbital speed relative to the Sun. But the same is true of both satellites of Mars - the orbital speed of Mars relative to the Sun is about 24 km/s, whereas the orbital speeds of Deimos and Phobos relative to Mars are about 1.4 km/s and about 2 km/s respectively. It must also be true for the outer moons of both Jupiter and Saturn - by my calculation, any moon of Jupiter beyond Europa and any moon of Saturn beyond Rhea has this property. So how is the phrase "Unlike all other moons in the solar system" justified ? Gandalf61 ( talk) 14:13, 12 March 2010 (UTC)
Primary | Satellite | p | d | p < d | p2 < d |
---|---|---|---|---|---|
Earth | Moon | 13 | 389 | Yes | Yes |
Mars | Phobos | 2,160 | 24,308 | Yes | No |
Mars | Deimos | 544 | 9,716 | Yes | No |
Jupiter |
Megaclite (outermost moon of Pasiphaë group) |
5.4 | 31.5 | Yes | Yes |
Saturn |
Fornjot (Outermost known moon) |
7.9 | 60.7 | Yes | No |
Uranus |
Ferdinand (Outermost known moon) |
10.7 | 137.7 | Yes | Yes |
In contrast to all texts that I have ever read, this maths site www.mathpages.com/home/kmath273.htm plausibly proposes that the moons orbit has not always been receding from Earth. I think that mention should be made of this in the article. I will likely be unable to pursue this matter as I rarely have appropriate internet access. 93.187.145.247 ( talk) 20:12, 11 September 2010 (UTC)
Both the earth and the moon carry stored Kinetic energy related to their orbital path around the sun. They also carry stored kinetic energy related to their orbital path around their center of gravity and rotation. However these values interact in such a manner as to allow the earth-moon system to perturb the sun orbit parameters of particularly the moon by adding to and subtracting kinetic energy (and angular momentum) from the moon's orbit around the sun during certain phases of its orbital path around the sun. This is presumably an important factor related to the ballistics of the moon's orbit around the sun, and explains why the moon speeds up and rises in orbit over the Earth's orbit radius during half the moons orbit, and then slows back down and passes back under the earth's orbit radius during the other half. Is there any discussion of this angular momentum transfer subject matter available to be read? WFPM ( talk) 02:31, 14 February 2011 (UTC)
Does that mean that that you think that there is no transfer of angular momentum to the moon and and then back to the earth during the period of the moons orbit around the earth? That's the idea that I'm trying to promote. WFPM ( talk) 15:00, 14 February 2011 (UTC) Then we can generate the idea that although the orbit of the moon is always around the sun, it includes 1 incidence where it advances over the top of the earth's orbit and another incidence where it slides back under the earth's orbit. And I'm thinking about the stability of such a situation. WFPM ( talk) 15:08, 14 February 2011 (UTC)
Interesting difference in concept!! So the Sun is in orbit around the sun. And the moon is on a point behind the earth along the path of the earth's orbit around the sun. And then the moon rises up and over the earth's orbit around the sun (during a 15 day period) and then is on a point ahead of the earth on the earth's orbital path around the sun. And then the moon drops down and back to a point between the earth and the sun, and then moves up and back to a position behind the earth in its path around the sun, (also within the next 15 day period) And the question is how it managed to do that. And I thought that that was because the gravitational force of the earth on the moon was able to speed up the velocity of the moon during a 15 day period so that so that it had sufficient angular momentum in its path such as to raise its radius of motion around the sun to be greater than that of the earth. Then during the next 15 day period it fell back behind the earth in orbit due to having lost back to the moon the change in angular momentum around the sun. I'll leave it there for now for any additional comments that you might want to make. Cordially, WFPM. WFPM ( talk) 21:19, 15 February 2011 (UTC)
Astronomy: Moon / Solar System Redirect‑class Low‑importance | ||||||||||||||||
|
To-do list for User:Rich Farmbrough/temp331: To-do list is empty: remove {{To do}} tag or click on edit to add an item. |
If things like "synchronous rotation" are to be kept, then it makes sense to rename this article to "The Moon (motion)" from the current "The Moon (orbit)". mdf 15:03, 11 July 2006 (UTC)
I had an argument with a friend who said that the distance between the earth and the moon was increasing. From what I know about physics, this is impossible. Orbital energy must be lost due to tides etc. However, he argued so convincingly that I came here to know for sure. If he is correct, I think it deserves a section in the article, if he is wrong, the decay rate of the orbit would be an interesting factoid to add to this article.
: Roguebfl 11:05, 25 August 2006 (UTC)Predictions suggest that the range will increase until the Earth and Moon become double synchronised, that is, both are tidally locked to one another. (So the Earth's day length would match the Moon's future orbital period of about 47 days, and the Earth-Moon distance would be about 550000km, compared to today's figure of 400000km). This won't occur for something like 50 billion years, by which point the Sun will be a white dwarf and will have passed through a red giant stage, which may result in the destruction of the Earth. [1]
In the heading Inclination of the rotation axis, this article explains the axial tilt as 6.69° to ecliptic (my emphasis).
However, in the table lower down Other properties of the Moon's orbit Mean inclination of lunar equator to ecliptic is listed at 1° 32' Roo60 12:50, 15 July 2006 (UTC)this is really confusing for some people
Proposal: Merge Earth and Moon with either The Moon's orbit or Tidal acceleration.
The result of the debate was merge with tidal acceleration. — Lunokhod 21:12, 4 December 2006 (UTC)
It has been suggested that Earth and Moon be merged with either The Moon's orbit or Tidal acceleration.
FOR: I am for the move for the following reasons
I think that the some portion of this material could be placed in The Moon's orbit, but that Tidal acceleration is where the bulk of it should go. Lunokhod 18:46, 22 November 2006 (UTC)
ALTERNATIVE: The Earth and Moon page mainly deals with tidal evolution of the orbit. That topic has been treated at length on a separate page: Tidal acceleration. So I propose to merge Earth and Moon with that page instead. Do change the link on this page though. Tom Peters 11:47, 23 November 2006 (UTC)
Recently the statement that Earth+Moon form a double planet has been reversed. That apparently has been done on the grounds that the COM lies within the Earth. That is only one possible criterium. IMNSHO it also is a poor one: if the Moon were twice as small but four times more distant, the COM would lie outside of the Earth, and the smaller Moon would be part of a double planet anyway? Asimov's proposal, based on the fact that the Moon orbits the Sun rather than the Earth (also looking at the actual shape of its orbit in space) makes more sense. Anyway, with even the concept of "planet" in confusion, I don't believe we have a solid base to securely classify E&M as a double planet or not. Tom Peters 10:45, 4 December 2006 (UTC)
Asimov's proposal of considering the Earth-Moon system a double-planet system is based, yes, on Moon's orbit around the Sun, Moon's size and mass in comparison to Earth's (only the Pluto-Charon system come close in proportions - that one fully recognised as a double-planet) and also (I believe this is the most important point) the "tug of war" (Asimov's name): Sun's gravitational pull on Earth is stronger than Earth's. This is true only for Moon among all other big satellites in Solar System (some of the outer, tyniest moons of Jupiter and Saturn also have this property), false even for Charon. It also makes me doubt that, if Sun would dissappear suddenly, Moon's orbit around Earth would continue as if nothing had happened. Since Sun's gravitational pull on the Moon is stronger than Earth's, I'd expect Moon decaying into a lower orbit in case the Sun dissappears. Can anyone support the claim that "nothing would happen" with some calculations, or providing an animation using "Gravity" or any other simulation program? Thanks —Preceding unsigned comment added by 148.244.69.177 ( talk) 22:54, 16 October 2007 (UTC)
Proposal: Rename The Moon's orbit to Orbit of the Moon.
The result of the debate was move. — Lunokhod 10:50, 7 December 2006 (UTC)
FOR I am for the proposed rename/move because (1) it is not wikipedia policy to have pages started with the word "the", and (2) when listing this page in an alphabetic list of see alsos, this topic falls under "the" (hence the reason for the naming policy). Lunokhod 21:26, 4 December 2006 (UTC)
Makes sense. I agree. Tom Peters 23:23, 4 December 2006 (UTC)
You know, I just came over here to propose that idea myself. 100% agree. The Moon's Geology, The Moon's Exploration etc. would look just as bad. Fine if we're writing in Swedish (Indiens flagga for Flag of India for example), but not English. Mithridates 02:10, 7 December 2006 (UTC)
The perigee listed in the article may be good for an "average" month but the moon has been known to come as close as 356,300 km. Someone should find a better source. Sagittarian Milky Way 05:00, 23 March 2007 (UTC)
356337.064 -2338 Nov 09 03:22:22 356349.827 -2683 Nov 13 02:33:02 356352.945 -1055 Nov 13 21:40:37 356354.171 -2665 Nov 23 13:31:54 356356.491 -0851 Dec 08 02:26:27 356356.657 -2356 Oct 28 16:22:36 356360.917 -1400 Nov 17 21:11:04 356365.136 -2320 Nov 19 14:21:41 356365.621 796 Dec 19 05:44:44 356366.204 -2869 Oct 30 08:25:51
370389.858 -0367 Nov 19 13:58:27 370390.249 -2915 Nov 20 20:59:18 370391.003 -2588 Nov 05 10:27:44 370392.976 -0256 Dec 06 21:55:54 370393.790 -2699 Oct 18 19:22:03 370394.088 90 Dec 03 02:19:14 370395.483 -2933 Nov 08 21:26:07 370397.683 -1212 Nov 16 20:04:09 370404.210 -2088 Nov 11 23:55:44 370407.525 -1650 Nov 15 01:16:01
I see from the article that the ellipse of the lunar orbit rotates counterclockwise, and that the precession of its orbital plane is clockwise. How about the orbit itself? The animation of the Moon as it cycles through its phases allows one to infer that the orbit is counterclockwise (same as the rotation of the Earth, and the Earth's orbit around the Sun) but this really should be stated explicitly both here and at Moon. -- Wfaxon 22:01, 28 July 2007 (UTC)
Someone looking for info on the "secular acceleration of the Moon" in Wikipedia will search long and hard. Perhaps it is here but searching on this familiar term yields nothing. Cutler 09:51, 24 August 2007 (UTC)
The equations which are said to be the basis of the image are not clear. In the first place the given equations of the earth's orbit would describe a circle, not an ellipse? This is easily corrected and should be shown as precisely as possible in an encyclopedia article. In the second place, the origin of the symbol " p:(synodic months+1)=14 " is not clear. If "p" is a constant(14), then how can it be an integer? Should it be more precisely the number of synodic months in a sidereal year ~12.368? And why plus one? Will the contributor of this image and these equations please clear this up? PSpace —Preceding unsigned comment added by Alexselkirk1704 ( talk • contribs)
I've searched the internet, and can only find recorded dates for one of the lunar cycles, the synodic. This is a problem due to the importance of the draconic (nodical) cycle in predicting eclipses. Someone should do some research. 68.144.80.168 ( talk) 08:00, 30 March 2008 (UTC)
According to this article, cited by a source I can't access, the Earth and the Moon will achieve spin orbit resonance in 2 billion years. This seems a remarkably short time. I've heard estimates as high as 50 billion years. Serendi pod ous 16:08, 8 June 2008 (UTC)
There are two changes under discussion with both being in the Orbit of the Moon#Path of Earth and Moon around Sun section.
(Unindent otherwise the lists below get really to read.) The distinction is made on both the convex and concave polygons and convex set articles in that they note that the observer's position is inside the shape when taking the measurements that determine if it's convex or concave.
I have two questions:
While pondering that; Here are definitions from my dictionary starting with convex. The italics are my comments.
That's it for the convex definitions. Here is concave
The point is that when words like convex and concave are used care is taken to note the observer's position, and if needed, the orientation of the subject described.
This is why I commented on the illustration caption. The caption itself fails to orient the observer and then in parentheses leads the reader, and presumed observer, to a spot where the subject would be interpreted as concave per any of the dictionary definitions. This is why I suggested that the illustration caption be changed to “From the point of view of the Sun (far left down), the Earth and Moon's path around the Sun is always concave.”
An alternative wording: "The area inside the Moon's orbit around the Sun forms a convex set. The sun is to the far left and down." Or, "Detail of the Moon plus Earth system as it orbits the Sun which would be to the far left and down. The orbit is convex when viewed from the outside (upper right corner)." Either attempt to use convex correctly seems more convoluted than identifying where both the Sun and observer are and calling the Moon's path concave.
I'll see if I can make a better image. I found the web site it was stolen from a bit ago but would need to Google that one up again. -- Marc Kupper&;;;;;;;;#124; talk 01:58, 26 March 2009 (UTC)
[From Terry0051:] I agree with all of Marc's answers to the modified questions quoted as follows (with clarifications as offered below):-
"Q1: Do you think the Moon's path around the Sun is concave when looking inward at the entire Moon/Earth/Sun system? A: No.
"Q2: Do you think the Moon's path around the Sun is concave when looking outward from the POV of the Sun? A: Yes.
"Q3: Do you think the Moon's path around the Sun is convex when looking inward at the entire Moon/Earth/Sun system? A: Yes if you you view part of the orbit and treat it as an open curve) and "sort of" if you look at the entire system as the correct term is that we what the orbit defines is a convex set and not just "convex."
"Q4: Do you think the Moon's path around the Sun is convex when looking outward from the POV of the Sun? No.
The clarifications offered are:
A: We are talking about the Moon's curved path, relative to a non-rotating solar-system-barycentric reference frame - or heliocentric reference frame. (For the present purpose it does not matter which.)
B: All of the above answers have been given from the physical POV of an observer located either near the Sun, or else at a great distance away and from somewhere on or near the solar system's invariable plane.
C: None of the above answers have been given from the physical POV of an observer located on the Moon's path itself, and in relation to the small element of that path which is close to the observer (which seems to match the 'open curve' referred to in Marc's answer 3). (A physical POV located on the path-element is the one effectively used in the online astronomical references provided.)
D: Every element of the Moon's orbital path has its own curvature and center of curvature -- regular sources on calculus and orbital dynamics provide. From the physical POV of an observer located on this curved path-element, it is concave towards its center of curvature, and convex away from its center of curvature. This corresponds with the usage of concave and convex that occurs in the astronomical references already supplied.
E: There is no reason to believe the Moon's path is precisely periodic, many reasons to believe it is not, and it seems unnecessary for present purposes to go into the long-term behavior. The local curvature of the path-element that the Moon is traversing right now is defined by the dynamics of the Moon's position right now. Also, the motion is not, in physical fact, confined precisely to a single plane. These astronomical facts, and the probable absence of any closed curve for the orbital path, also make the language of convex sets seem somewhat alien from the physical situation under discussion.
As I read the original text, its task was to convey, in brief and less-technical language, the physical fact that the center of curvature of every element of the Moon's curved orbital path (in the non-rotating reference frame of the solar-system barycenter) is always on the inward side, towards the Sun, and there is no inwards-outwards alternation as the Moon makes its progress along its path.
The purpose of making this whole point seems to have been to convey, that while intuitive thinking might indicate that the center of curvature of the Moon's path at new-moon is away from the Sun and towards the Earth, that is not in fact so.
The less-technical language omitted a number of details, such as, that the center of curvature is not precisely in the Sun-Earth-Moon plane, nor in any other single plane. That simplification seems reasonable in a brief description, because the out-of-plane deviations remain small enough to neglect for this purpose. That is, the component, in the line from Moon to Sun, of the direction vector from the Moon towards the center of curvature of the path-element that the Moon is currently traversing, always points M->S, never the other way.
But it looks as if the recent edits have uncovered a point in the simplified language used in the original article, which was unclear to the general reader: i.e. the usage and physical POV of 'convex' and 'concave' -- even though these were clear to the authors of the cited mathematical-astronomy references, and to others familiar with the calculus of orbital dynamics.
I still think it is clear that the original text, before the recent edits, was correct -- given prevailing usages of the words employed in the mathematical-astronomy field -- and is now in error. But I agree that it would be helpful if the text on this point is given brief and correct clarification. If the words chosen differ from those that are usually encountered in the astronomical refernces, it would also be helpful to let the reader know in some way what to expect as the usage in the outside world if s/he is interested enough to look up the cited astronomical references.
I suggest to Shaheenjim that he looks at the Godfray and Turner references which are online and only need one click of the mouse to reach. Terry0051 ( talk) 15:58, 26 March 2009 (UTC)
[From Terry0051]: Marc, there is a more informative definition in " Wiktionary - convex" "curved or bowed outward". This shows clearly that the current wording in the article "convex towards the Sun" is clearly wrong, it would mean 'curved or bowed outward towards the Sun'.
The way Shaheenjim has put it, "a distinction between convex/concave when looking outward from the inside, and convex/concave when looking inward" is both a confusing formulation in itself, and not the way in which the point has been formulated, whether in the references, in the article, nor by the other participants in the discussion. It would be more helpful to the discussion to use one of the clearer formulations on record.
The ostensible 'conflict' based on the use of the words 'convex' and 'concave' has already been explained as not a conflict, based on the differing physical POV relative to which the words were applied. Please look again at the Vacher reference, page 5, Fig. 2B, and the description "everywhere convex outward", and then compare that with Turner, page 119, where it is made clear in connexion with an idealized case in which the moon moves around the sun in a circle, that is an example of a path that is 'always concave to the sun'. I am sure that you can see very easily how those two statements can be made about the same curve without being in conflict.
The Turner and Godfray references are both in the mainstream astronomical literature, and it would be well if the general reader is alerted, at least in a footnote, to expect their usage, for the reason already offered. The orbit of the moon is not a closed curve and better descriptions of its curvature would probably be given in terms that include center of curvature and curvature. Terry0051 ( talk) 20:35, 26 March 2009 (UTC)
[From Terry0051] Thank you Shaheenjim for your further edit, and I agree with it as far as it goes, but it leaves the ambiguity in 'convex' unaddressed. I was about to do something almost the same, retaining the word 'convex', along with a clarifying phrase based on Marc's answer #3, plus a footnote that advises of the alternative usage in respect of the same geometry. The clarifying phrase, and the explanatory footnote, I've now put in. I believe this is securely sourced in the cited references and hope and believe it otherwise reflects common ground between parties to the current discussion. Terry0051 ( talk) 21:14, 26 March 2009 (UTC)
As the Moon orbit becomes larger, eventually the year will become exactly 12 synodic (or 13 sideric) months. Will this cause any resonance effect, like the orbit getting more excentric, or is the orbit too irregular for such resonance effects? Ambi Valent ( talk) 23:52, 30 April 2009 (UTC)
The diagram in the section "Path of Earth and Moon around Sun" only shows a small part of the orbit of the Moon relative to the Sun, in order to illustrate the "convexity" (or "concavity") point. The diagram is not apt to illustrate the direction of movement of the Moon along its orbit (and in any case, insufficient information is given to define this direction, because the diagram might equally be considered as seen from the north, or from the south). But to clarify the "convexity" point, it is important to say what is the location of the Sun relative to the portion of orbit shown in the diagram: the Sun is located below and to the left. Terry0051 ( talk) 12:33, 2 May 2009 (UTC)
Joe and Terry: The diagram of lunar orbit 'convexity/concavity' you prefer has been around for at least a hundred years, since Young's 1902 Manual of Astronomy. Considering the voluminous discussion above about whether your reverted diagram makes clear orbital direction and whether viewed from up, down, inside or out I felt that the diagram I submitted made those key points absolutely clear to the casual reader of Wikipedia. Perhaps you would care to clarify your objections to describing the orbit as a modified cycloid and why the diagram that shows this is unacceptable? Geologician ( talk) 10:16, 26 June 2009 (UTC)
[From Terry0051]Hallo Sagittarian Milky Way:-- Yes, I believe you're completely correct in your reading of the text, fwiw I agree with you that's what the author meant.
Hallo again Geologician:
-- A direct quote of an isolated sentence is out of context if it doesn't take account of the overall message, what the text as a whole is talking about. You didn't take the overall message into account, your isolated sentence was out of context.
-- (Also, there's something like assuming good faith, giving the author reasonable credit, assuming that he probably had some sense and probably wasn't trying to say a crazy thing that nobody ever believed, and choosing a sensible reading of the whole if one is available. If a reading doesn't do that, it may end up looking like a perverse reading.)
-- I agree that Young (in its original form) is a 'reliable source' under the usual conditions: but that doesn't apply to any altered version.
-- You misquote me more than once, (a) I didn't deny Young as a reiable source and (b) I didn't say that the sign of the curvature 'cannot' change, only that there are proofs here that it does not change: those proofs are in the cited articles where they show that the orbit is always concave. It doesn't appear reasonable for you to assert that there is 'no supporting evidence'. But your suggestion that Young's statements apply only to 'an individual synodic month segment' does appears to be an invention of something not present in Young or anywhere else at all.
-- Where is your reliable source for 'judicious exaggeration'? I would say that whatever may be 'judicious' exaggeration, changing the shape is not, and the onus is on an editor who wants to 'exaggerate' to find RS in support.
-- You haven't shown any reliable source for the cusps, and your diagram does not resemble any of the diagrams in the reliable sources -- please read Sagittarian Milky Way's very good description of the real characteristics or the orbit by somebody who does 'get the point': [Quote: "all that is within the power of the Moon's feeble orbital speed of it's own to do is shallow up the radius of curvature of it's still concaveness to that of a 1.5 AU orbit's (temporarily of course, no spiral) instead of the nominal 1 AU radius."] Terry0051 ( talk) 23:56, 28 June 2009 (UTC)
None of your cases represent the Moon's path. Only n=13.37 and b=a/389 do (which Turner approximates in case 3 as n=13 and b=a/400). Turner's cases 1 and 2 do not represent the Moon's orbit. I have already stated many times that other moons can have any conceivable orbital shape relative to the Sun, including hypothetical and unrealistic exaggerations of the Moon's present orbit—those that maintain 12.37 synodic months per year regardless of size even though those orbits violate the universal theory of gravity. In my "exaggerating" discussion above I stated that if the Moon's orbital radius is increased beyond b=a/169.4 (while maintaining n=13.37) it developes a bulge inward, which means it ceases to be everywhere convex outward. This only shows that Turner's model is correct because it can generate all possible orbits, including the Moon's orbit whose convex outward shape is only possible with parameters near those of the Moon's actual orbit. — Joe Kress ( talk) 03:52, 3 July 2009 (UTC)
[From Terry0051] I believe it's relevant to the improvement of the main article to give cross-references here to the following two matters (especially because of the amount of editorial efforts that have been put into this section here, and because of the length and character of the discussion):
Recent change was said to be a 'correction' from 1.023 'km/s' to 'm/s'. Mean distance from the Earth is about 385000 km (not m), mean sidereal period is 27.321661 days of 86400 secs, (385000 x 2 π )/(27.321661 x 86400) comes to about 1.024 in km/s not m/s. After a chance for anybody to point out mistakes in this , the 'correction' should be reverted. Terry0051 ( talk) 22:47, 1 December 2009 (UTC)
In Path of Earth and Moon around Sun the article says "Unlike all other moons in the solar system, the trajectory of the Moon is very similar to that of the Earth". In context, I assume this refers to the fact that the motion of the Moon as viewed from the Sun is never retrograde. This is a consequence of the fact that the Moon's orbital speed relative to the Earth is smaller than the Earth's orbital speed relative to the Sun. But the same is true of both satellites of Mars - the orbital speed of Mars relative to the Sun is about 24 km/s, whereas the orbital speeds of Deimos and Phobos relative to Mars are about 1.4 km/s and about 2 km/s respectively. It must also be true for the outer moons of both Jupiter and Saturn - by my calculation, any moon of Jupiter beyond Europa and any moon of Saturn beyond Rhea has this property. So how is the phrase "Unlike all other moons in the solar system" justified ? Gandalf61 ( talk) 14:13, 12 March 2010 (UTC)
Primary | Satellite | p | d | p < d | p2 < d |
---|---|---|---|---|---|
Earth | Moon | 13 | 389 | Yes | Yes |
Mars | Phobos | 2,160 | 24,308 | Yes | No |
Mars | Deimos | 544 | 9,716 | Yes | No |
Jupiter |
Megaclite (outermost moon of Pasiphaë group) |
5.4 | 31.5 | Yes | Yes |
Saturn |
Fornjot (Outermost known moon) |
7.9 | 60.7 | Yes | No |
Uranus |
Ferdinand (Outermost known moon) |
10.7 | 137.7 | Yes | Yes |
In contrast to all texts that I have ever read, this maths site www.mathpages.com/home/kmath273.htm plausibly proposes that the moons orbit has not always been receding from Earth. I think that mention should be made of this in the article. I will likely be unable to pursue this matter as I rarely have appropriate internet access. 93.187.145.247 ( talk) 20:12, 11 September 2010 (UTC)
Both the earth and the moon carry stored Kinetic energy related to their orbital path around the sun. They also carry stored kinetic energy related to their orbital path around their center of gravity and rotation. However these values interact in such a manner as to allow the earth-moon system to perturb the sun orbit parameters of particularly the moon by adding to and subtracting kinetic energy (and angular momentum) from the moon's orbit around the sun during certain phases of its orbital path around the sun. This is presumably an important factor related to the ballistics of the moon's orbit around the sun, and explains why the moon speeds up and rises in orbit over the Earth's orbit radius during half the moons orbit, and then slows back down and passes back under the earth's orbit radius during the other half. Is there any discussion of this angular momentum transfer subject matter available to be read? WFPM ( talk) 02:31, 14 February 2011 (UTC)
Does that mean that that you think that there is no transfer of angular momentum to the moon and and then back to the earth during the period of the moons orbit around the earth? That's the idea that I'm trying to promote. WFPM ( talk) 15:00, 14 February 2011 (UTC) Then we can generate the idea that although the orbit of the moon is always around the sun, it includes 1 incidence where it advances over the top of the earth's orbit and another incidence where it slides back under the earth's orbit. And I'm thinking about the stability of such a situation. WFPM ( talk) 15:08, 14 February 2011 (UTC)
Interesting difference in concept!! So the Sun is in orbit around the sun. And the moon is on a point behind the earth along the path of the earth's orbit around the sun. And then the moon rises up and over the earth's orbit around the sun (during a 15 day period) and then is on a point ahead of the earth on the earth's orbital path around the sun. And then the moon drops down and back to a point between the earth and the sun, and then moves up and back to a position behind the earth in its path around the sun, (also within the next 15 day period) And the question is how it managed to do that. And I thought that that was because the gravitational force of the earth on the moon was able to speed up the velocity of the moon during a 15 day period so that so that it had sufficient angular momentum in its path such as to raise its radius of motion around the sun to be greater than that of the earth. Then during the next 15 day period it fell back behind the earth in orbit due to having lost back to the moon the change in angular momentum around the sun. I'll leave it there for now for any additional comments that you might want to make. Cordially, WFPM. WFPM ( talk) 21:19, 15 February 2011 (UTC)