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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.
No - the point is that energy is not conserved ! The sum of the moon's potential energy and kinetic energy falls as energy is progressively dissipated in the tides. Paradoxically the result is to increase the moon's potential energy at the cost of its kinetic energy. Perhaps this is what is intended above. g4oep
Roguebfl 11:01, 25 August 2006 (UTC)
: 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)
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)
The equations which are said to be the basis of the image would describe a circle, not an ellipse. The image should be shown as precisely as possible in an encyclopedia article. I have written a python program to display the image of the orbit of the Earth and Moon together. This program uses the correct values for the masses, distances, velocities and acceleration according to Newton's law of gravity and therefore shows a true representation of the path of the Earth and Moon together to scale. It does consider the Earth-Moon-Sun as a three-body system and so disregards the gravitational effects of the other planets. This program can be found at http://paste.debian.net/44587/ it requires python 2 or 3 with numpy and matplotlib. I would to include this in the article, both the image or a portion of it, and the equations used to calculate it. I am uncertain how to do this. If someone agrees to help with this please contact me alexselkirk1704@hotmail.com
Alexselkirk1704 ( talk) 04:33, 22 September 2013 (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)
In its orbit around the sun the moon would have to have its orbital velocity be faster than the earth's orbital velocity for the moon to rise up and passover the earth's orbit. And it would have acquired that increased velocity (and angular momentum) from the earth. That sounds like an exchange in angular momentum to me. WFPM ( talk) 14:06, 1 April 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 Earth 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)
When object A is the primary gravitational influence on object B, then B is said to orbit A. Even if both those objects are orbiting another body, the terminology still holds. Consider a satellite placed into orbit around the moon. That satellite will indeed go around the earth in a nearly-elliptical path because it is gravitationally attached to the moon, but we do not say that it is orbiting the earth. Likewise, our Sun is orbiting the mass in the center of the galaxy, but the Earth is not said to orbit that mass--it orbits the Sun.
Occasionally objects have complex enough motion that they do not truly orbit one body, but this is extremely rare in nature, as multi-body motion is generally not very stable. Kemperb ( talk) 19:17, 11 March 2011 (UTC)
Yes, but that was the reason Galileo made his point about the planets of Jupiter, because they were definitely orbiting Jupiter faster than the system was orbiting the sun. Ergo the logic of the Jupiter/Satellite angular momentum transfer concept. And it's also the case with the Earth/moon system, only less apparent. But the Earth/moon system looks doubtfull for long time stability, except for the evidence. WFPM ( talk) 01:26, 14 March 2011 (UTC)
In light of the recent tsunami (11 Mar 2011) and talk of how it could have been influenced by the "supermoon", it seems like some discussion of this topic is in order. As an orbit dynamicist (but admittedly not an astrophysicist), I am concerned by claims in the article that supermoons are correlated (or might be correlated) to significant geological and meteorological events. These claims are completely uncited, and as a scientist I cannot think of a good reason that lunar perigee coinciding with full moon would have more impact than, say, perigee + new moon. The events quoted have been cherry-picked to match, and they don't even match well. (One deleted event was two weeks before a "supermoon"--i.e. when the moon was at apogee!) I propose removing the speculative sections, leaving only a discussion of the term and its history, and will do this unless I can be swayed otherwise. Kemperb ( talk) 18:31, 11 March 2011 (UTC)
To be fair, does anyone have an argument against deleting the section? — Tamfang ( talk) 02:38, 12 March 2011 (UTC)
"and the 8.9-magnitude earthquake and subsequent tsunami that hit Japan on March 11, 2011, was eight days prior to a Super-Moon during which the moon was reported to be closer to the Earth than at any time since 1992"
The super moon stuff seems a bit fringe, but okay - but this part is really silly as it is completely opposed to the supermoon theory - 8 days before a Super-Moon means the moon was further than average from the Earth (as it takes ~14 days to move from furthest to nearest point when it is moving towards us), and the three objects were well out of line, so even if the SuperMoon theory is correct, things happening days away from that particular date can't be part of the evidence of that theory, and things happening more than a week either side of a supermoon stand in direct contradiction with the theory. -- Sfnhltb ( talk) 01:13, 12 March 2011 (UTC)
The Article describes the rates of various motions and the shapes and sizes of their paths, but seems to say nothing about the current position along those paths.
For example, and approximating, it indicates that the Lunar North Pole, projected onto the Celestial Sphere, traces in 18.6 years a circle of radius 1.5° about the "pole of the ecliptic", which is at 18h +67°, but it gives no indication of when, in 2000 to 2018.6, the projected pole crossed 18h at 68.5 deg; and no clear indication of in which direction it was going (to higher or lower R.A.).
The "orbital pole" is indicated as moving similarly with a larger radius.
The Moon goes round its orbit once per relevant month, but the article gives no clue as to where the Moon actually is.
Commonly, other sites do no better.
I suggest that all of those motions can be expressed algebraically to first order either linearly or in terms of the sine and cosine of scaled time from a nearby epoch, which would be a good clear way to present the information. RA & Dec would serve to indicate the pole and the plane of the orbit. For the position, perhaps the distance along the ecliptic from a stated point, and the signed distance from the ecliptic. One might also indicate the stretch of time for which the simple expressions would be good to, say, one degree or 1%; and hope to update them when the mean error reached half that.
I cannot do this myself; I came to the Article to seek such information. 94.30.84.71 ( talk) 13:48, 24 March 2011 (UTC)
RA = 270 + 1.5 * sin(2 pi (Y-2004.39) / 18.6) Dec = 66.2 + 1.5 * cos(2 pi (Y-2004.39) / 18.6)
In the section on lunar standstill, some angular arithmetic is presented that must involve some rounding (23°29′ + 5°9′ or 28°36′) and later (23°28′ − 5°8′ or 18°19′). The first sum would be 28°38′ while the second would be 18°20′. I'm wondering if the (distracting) rounding in this description could be avoided somehow. Or, perhaps it simply reflects an error? Mike Fikes ( talk) 21:48, 5 August 2011 (UTC)
I have read through the entire article and I cannot find a statement of which way the Moon goes around the Earth. Please would someone add this, either in the introduction, or in the section: "Path of Earth and Moon around Sun".
I suggest a sentence in the form: "Viewed from the north, i.e. the direction of the star Polaris, the Moon travels [clockwise/anticlockwise] around the Earth; the Earth travels [clockwise/anticlockwise] around the Sun." Darkman101 ( talk) 17:26, 5 September 2011 (UTC)
This is still too technical for most encyclopedia users, and fails to answer a basic question of observers from the Earth: does the Moon rise in the East or the West? This is not just about the direction of orbit, it is about direction and speed of orbit, relative to the speed of Earth's rotation. A simple "The Moon rises in the East and sets in the West" should suffice (if my assumption is correct). Could someone with the expertise to make the deduction add such a statement in the appropriate place in the article? Thanks. FreeFlow99 ( talk) 11:22, 13 February 2019 (UTC)
I placed a Citation needed template in this section on the claim that the barycenter definition is a criterion. I just went through a search of this for the Double planet article and was unable to find anything on this claim that may be considered a reliable source. I removed the claim (after more than a year) from that article, and I will transfer it from this article to this talk page if a reliable source cannot be found.
One reason the barycenter criterion is not such a good idea is that it is too "time-specific". Since the Moon's orbit is constantly getting a little larger each year, the Earth-Moon barycenter is constantly getting closer to the surface of the Earth. So at some point in the future, when the barycenter is above Earth's surface, then by this criterion the "planet-moon" status will change to "double planet" status. So this criterion or definition is too time-specific and therefore can cause one type of system to turn into another type. – PIE ( CLIMAX ) 16:42, 20 January 2012 (UTC)
This page needs a Java or Flash applet that will show how the Moon, its nodes and apsids all rotate with different periods and in different directions. Prose can only explain so much; a moving model that can be viewed from different angles and different frames is essential here. 24.138.76.31 ( talk) 17:20, 8 June 2013 (UTC)
"some of the Earth's angular (or rotational) momentum is gradually being transferred to the Moon's orbital momentum, and this causes the Moon to slowly recede from Earth at the rate of approximately 38 millimetres per year."
I don't see anything about the change in the length of the month while changing the orbital radius. What is the change in the length of the month? — Preceding unsigned comment added by Reddwarf2956 ( talk • contribs) 04:22, 20 September 2013 (UTC)
The equations which are said to be the basis of the image in the article are not accurate. The image should be shown as accurately as possible in an encyclopedia article. I have written a python program to display the image of the orbit of the Earth and Moon together. This program uses the correct values for the masses, distances, velocities and acceleration according to Newton's law of gravity and therefore shows a true representation of the path of the Earth and Moon together. It does consider the Earth-Moon-Sun as a three-body system and so disregards the gravitational effects of the other planets. This program can be found at http://pastebin.com/NEpwDQxs It requires python 2 or 3 with numpy and matplotlib. Give it time to run. It takes about 26 seconds on my machine. The image of a portion of the earth moon orbit is here http://ctrlv.in/240322 The green curve is the earth orbit and the blue curve is the moon orbit. I would like to replace the image in the article with this image together with an explanation of the equations used to calculate it. I am uncertain how to do this. If someone agrees that this is a worthwhile addition and would like to help put it in, please let me know here.
B A Andersen ( talk) 13:46, 22 September 2013 (UTC)
There is said: "The Moon crosses the same node every 27.2122 days" (the draconic month) There should be said, that it is an average value, where actual time distances between ascending node passages (relative to dynamic ecliptic plane) are currently (this year) in range 27.05 - 27.36 days (the difference is over 7 hours), varying on a sinusoide with 173.3 day period, as detected from NASA/JPL ephemerides DE422. Similar variability (173 day sinusoide) shows the angle between angular momentum vector (orbit axis) of Moon orbit relative to Earth and of angular momentum vector of EMB orbit relative to Sun (on range 5.0328° - 5.30428°). The angular frequency of rotation of a vector from EMB to Moon Ascending Node ranges from 1.6e-5° to 3.21° per 27 days (the low bound could be probably an artifact of discrete position of ascending node calculation? But probably it is not...). I found no mention of the variability of Moon precession here...?! There should be at least the word average draconic month... P.A.Semi — Preceding unsigned comment added by 79.98.159.114 ( talk) 22:45, 18 October 2013 (UTC)
The article says, The sidereal month is the time it takes to make one complete orbit of the earth with respect to the fixed stars, it is about 27.32 days
and later The time between two successive passes of the same ecliptic longitude is called the tropical month. The latter three periods are slightly different from the sidereal month
The sidereal month and the tropical month both refer to one revolution in ecliptic longitude, and in both cases use the rate of change of the mean longitude at an instant. The difference is that the sidereal month refers to a fixed equinox, the tropical year to the equinox of date. Usually the instant and, in the first case date of fixed equinox, J2000.
Simon et al. have 1732559343.736 arcseconds per Julian century. [1]For the J2000 equinox. There being 36525 days in a Julian century and 1296000 arcseconds per revolution, we get 27.32166155 days. Same thing the article gives for the sidereal month.
The same calculation for the mean elements of date agrees perfectly with the tropical month. And it has nothing to do with the vernal equinox. Saros136 ( talk) 08:54, 12 August 2014 (UTC)
I am new to wikipedia and I added a diagram I thought would be helpful. However, I think I have messed up the formmating on the TOC and table at the beginning of this page. Can someone please fix it and let me know what I can do in the future to avoid this? Thank you! -Peter Psobchak ( talk) 23:00, 3 October 2014 (UTC)
Thanks for the input and for helping me on the formatting. I will go ahead and update that spelling error and put in an updated version of the diagram. As for the sourcing, I used the angular data available on this page, and cross-checked it against data from NASA Jet Propulsion Laboratory and they both matched up. I was just trying to illustrate the numbers available on this page in a way that was easier to understand. I will need to look into how I cite sources. Psobchak ( talk) 13:45, 6 October 2014 (UTC)
I replaced the above diagram with this more illustrated version from NASA. It shows all figures except for the angle between the ecliptic and the lunar equator (1.54 degree). Hope that's not too frustrating to the author of the original image. Rfassbind – talk 00:17, 22 August 2015 (UTC)
I would argue that my original image is less cluttered and is easier to read, I am not sure that the new image adds much more to the conversation other than a graphical depiction of the earth and the moon. I find it to be a bit harder to read. I am open to others suggestions on this subject. Psobchak ( talk) 21:26, 12 January 2016 (UTC)
Since the NASA image is now posted twice in this article, I am adding back in the original diagram that I made so that we have the best of both worlds. Additionally, it appears other agree that my diagram contains some good information, I have updated it to fix some spelling errors as well. Again, I am open to feedback on this being the right decision. Psobchak ( talk) 19:05, 3 October 2017 (UTC)
References
Is this a typo? 74.72.169.238 ( talk) 21:52, 19 November 2014 (UTC)
Article is written with Km all over it. Where I live, we work with miles, inperial measurements. I'm struggling with this article because the Km does not quantify the distances. The article and associated articles need updating to show both measurement systems. — Preceding unsigned comment added by 217.35.255.84 ( talk) 12:34, 17 October 2016 (UTC)
All the content pertaining the Tidal rhythmites has no references whithin and they had to be seen on
Tidal acceleration
The citation is Williams, G. "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics 38, 37 (2000).
The contents on the Earth's paleorotation and distance to the Moon is contradicted in a posterior document [1] consulted here Citing from the abstract: "We have shown that analysis of ancient tidal rhythmite may help us to estimate the palaeolunar orbital periods in terms of lunar days/month accurately. Determination of absolute Earth–Moon distances and Earth’s palaeorotational parameters in the distant geological past from tidal rhythmite, however, is ambiguous because of the difficulties in determining the absolute length of the ancient lunar sidereal month." (my bold)
The same concern about the contents and references should be addressed in the Tidal acceleration page.
The page Rhythmite#Tidal_rhythmites is correct because there is no mention of this outdated and erroneous content.
Because I'm not used to edit WP I ask a more experient editor to proceed with the corrections.
62.169.67.133 ( talk) 00:47, 4 November 2016 (UTC)
References
Under "Elliptic shape", the phrase "Julian day 2000" might be a mistake. It might be "Epoch 2000".
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Ouu;it in and get to go in — Preceding
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Can someone please add this info about the orbit of the Moon and the Earth's atmosphere? link: [4]. Thank you. -- Miaow 15:10, 26 February 2019 (UTC)
"Semi-major axis[1] 384,748 km (239,071 mi)[2]
Inverse sine parallax[5] 384,400 km (238,900 mi)"
The Semi-major and an 'Inverse sine parallax' is just the same number = 384400 !
And the number: 384,748 km is a hypothetical semi-major axis only; because for the isolated/idealised case of Moon-Earth without any perturbations (mainly of the Sun).
Simply: T = 2pi (a^3/G(M+m))^0.5 = 27.322 days, for a = 384748 km.
Under "Properties" and "Elliptic shape", the phrase "(Julian day 2000)" might be a mistake. — Preceding unsigned comment added by 2A00:23C4:7C87:4F00:A90D:559:F0F0:6602 ( talk) 12:50, 12 August 2020 (UTC)
This diagram claim to be to scale but clearly isn't. For example the earth is ~3.6 times bigger than the moon, in the diagram it's ~2 time bigger. The orbit size compared to the earth size is also wrong. For whatever reason Wikipedia won't let me upload an image with the correct sizes. — Preceding unsigned comment added by Lebesnec ( talk • contribs) 13:25, 30 April 2021 (UTC)
I wonder if anyone can confirm if this research is accurate - I can't find online copies of the obscure citations in fn.27 - On the curve of the Moon’s orbit: A brisk debate between gentlemen, the Trajectorium Lunare and after:
https://www.academia.edu/13219527/On_the_curve_of_the_Moons_orbit_a_brisk_debate_between_gentleman_the_Trajectorium_Lunare_and_after?auto=download
"The final steps towards a mathematical proof of the question were taken in 1761. In a short article, comprising just two pages of textual argument and one diagram the proof was provide[d] by ‘S. Reader, Mathematical’. The article appeared in the January 1761 issue of the somewhat eccentric journal Martin’s Miscellaneous Correspondence.(27) ... No specific reason is given for the timing of the publication, but Benjamin Martin (the Editor) provides the following introduction, ‘I was favoured with the following Theory, by an ingenious and learned Friend at Wareham, some Years ago’. The article is with little doubt due to the Reverend Simon Reader (? – c. 1794), who was well-known at that time as a Dissenting Minister, preaching at Wareham, in Dorset. Apparently, therefore, the article and proof were produced some time prior to 1761, but the exact date remains unclear. Reader provides no references or historical con-text within his article, and simply sets out to prove the introductory statement that: ‘A Demonstration that the Moon passes, at the Time of Conjunction; further from the Sun, than a right Line, drawn betwixt two of its Places, taken, one before and the other after Conjunction, and equidistant from I’’. The Proof is entirely geometrical, and having es-tablished the correctness of the statement, a corollary then asserts that the Moon’s path must be concave to the Sun. Reader’s proof is similar in outline to that provided by John Badder in January of 1743, but rather than relying upon approximate numerical calculations Reader develops a full analytic argument... The same obscurity has additionally befallen the Reverend Simon Reader, who apparently provided the first mathematical proof that the Moon’s path must always be concave towards the Sun. Indeed, the proof of the concavity of the Moon’s path, if even stated with an astronomy text, is invariably taken as being in the ‘public domain’ with no original authorship being recognized." [fn.27: Martin’s Miscellaneous Correspondence, Vol. 4, p. 591, January 1761. There is little biographical data on Simon Reader. According to the memoir of the Reverend W. Hordle (The Evangelical Magazine and Missionary Chronicle, 28 (1850), p. 628 ‘he ran a boarding school and taught Latin, Greek, geography, the use of globes and astronomy’. Reader was educated under Rev. Dr Philip Doddridge (1702-1751) – a leading English Nonconformist minister - and is described as being, ‘a man of extensive learning’ in The Critical Review, Or, Annals of Literature for November, 1795 (p. 319).] Shtove ( talk) 20:02, 16 May 2021 (UTC)
According to this section, libration in longitude is maximal at apogee and perigee. This should be rate of libration, since these are the points where rotational angular speed and orbital angular speed differ most - the amplitude is surely zero at these points. I would edit it myself but am struggling with calculation of the points on the orbit where the angle of libration is maximal - this is where the rate is zero, which is when orbital angular speed is equal to mean orbital angular speed. Or have I lost my marbles?
An editor has identified a potential problem with the redirect
Earth-moon system and has thus listed it
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Mathglot (
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03:00, 14 October 2022 (UTC)
An image caption in section History of observations and measurement now reads, "The apparent trajectory of the Moon in the sky seen from Earth each night is like a wide ellipse, ... ". Isn't it very close to a great circle on the celestial sphere, at most 1°1′32″ off? The difference is too small to be observed without instrumentation, so why call it an ellipse? -- Lambiam 13:49, 28 June 2023 (UTC)
In effect, this means that the " tropical year" on the Moon is only 347 days long. This is called the draconic year or eclipse year.
Is that so? It's not obvious to me that the precession of the Moon's rotation axis should match that of its orbital plane. —Tamfang ( talk) 18:07, 10 April 2024 (UTC)
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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.
No - the point is that energy is not conserved ! The sum of the moon's potential energy and kinetic energy falls as energy is progressively dissipated in the tides. Paradoxically the result is to increase the moon's potential energy at the cost of its kinetic energy. Perhaps this is what is intended above. g4oep
Roguebfl 11:01, 25 August 2006 (UTC)
: 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)
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)
The equations which are said to be the basis of the image would describe a circle, not an ellipse. The image should be shown as precisely as possible in an encyclopedia article. I have written a python program to display the image of the orbit of the Earth and Moon together. This program uses the correct values for the masses, distances, velocities and acceleration according to Newton's law of gravity and therefore shows a true representation of the path of the Earth and Moon together to scale. It does consider the Earth-Moon-Sun as a three-body system and so disregards the gravitational effects of the other planets. This program can be found at http://paste.debian.net/44587/ it requires python 2 or 3 with numpy and matplotlib. I would to include this in the article, both the image or a portion of it, and the equations used to calculate it. I am uncertain how to do this. If someone agrees to help with this please contact me alexselkirk1704@hotmail.com
Alexselkirk1704 ( talk) 04:33, 22 September 2013 (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)
In its orbit around the sun the moon would have to have its orbital velocity be faster than the earth's orbital velocity for the moon to rise up and passover the earth's orbit. And it would have acquired that increased velocity (and angular momentum) from the earth. That sounds like an exchange in angular momentum to me. WFPM ( talk) 14:06, 1 April 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 Earth 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)
When object A is the primary gravitational influence on object B, then B is said to orbit A. Even if both those objects are orbiting another body, the terminology still holds. Consider a satellite placed into orbit around the moon. That satellite will indeed go around the earth in a nearly-elliptical path because it is gravitationally attached to the moon, but we do not say that it is orbiting the earth. Likewise, our Sun is orbiting the mass in the center of the galaxy, but the Earth is not said to orbit that mass--it orbits the Sun.
Occasionally objects have complex enough motion that they do not truly orbit one body, but this is extremely rare in nature, as multi-body motion is generally not very stable. Kemperb ( talk) 19:17, 11 March 2011 (UTC)
Yes, but that was the reason Galileo made his point about the planets of Jupiter, because they were definitely orbiting Jupiter faster than the system was orbiting the sun. Ergo the logic of the Jupiter/Satellite angular momentum transfer concept. And it's also the case with the Earth/moon system, only less apparent. But the Earth/moon system looks doubtfull for long time stability, except for the evidence. WFPM ( talk) 01:26, 14 March 2011 (UTC)
In light of the recent tsunami (11 Mar 2011) and talk of how it could have been influenced by the "supermoon", it seems like some discussion of this topic is in order. As an orbit dynamicist (but admittedly not an astrophysicist), I am concerned by claims in the article that supermoons are correlated (or might be correlated) to significant geological and meteorological events. These claims are completely uncited, and as a scientist I cannot think of a good reason that lunar perigee coinciding with full moon would have more impact than, say, perigee + new moon. The events quoted have been cherry-picked to match, and they don't even match well. (One deleted event was two weeks before a "supermoon"--i.e. when the moon was at apogee!) I propose removing the speculative sections, leaving only a discussion of the term and its history, and will do this unless I can be swayed otherwise. Kemperb ( talk) 18:31, 11 March 2011 (UTC)
To be fair, does anyone have an argument against deleting the section? — Tamfang ( talk) 02:38, 12 March 2011 (UTC)
"and the 8.9-magnitude earthquake and subsequent tsunami that hit Japan on March 11, 2011, was eight days prior to a Super-Moon during which the moon was reported to be closer to the Earth than at any time since 1992"
The super moon stuff seems a bit fringe, but okay - but this part is really silly as it is completely opposed to the supermoon theory - 8 days before a Super-Moon means the moon was further than average from the Earth (as it takes ~14 days to move from furthest to nearest point when it is moving towards us), and the three objects were well out of line, so even if the SuperMoon theory is correct, things happening days away from that particular date can't be part of the evidence of that theory, and things happening more than a week either side of a supermoon stand in direct contradiction with the theory. -- Sfnhltb ( talk) 01:13, 12 March 2011 (UTC)
The Article describes the rates of various motions and the shapes and sizes of their paths, but seems to say nothing about the current position along those paths.
For example, and approximating, it indicates that the Lunar North Pole, projected onto the Celestial Sphere, traces in 18.6 years a circle of radius 1.5° about the "pole of the ecliptic", which is at 18h +67°, but it gives no indication of when, in 2000 to 2018.6, the projected pole crossed 18h at 68.5 deg; and no clear indication of in which direction it was going (to higher or lower R.A.).
The "orbital pole" is indicated as moving similarly with a larger radius.
The Moon goes round its orbit once per relevant month, but the article gives no clue as to where the Moon actually is.
Commonly, other sites do no better.
I suggest that all of those motions can be expressed algebraically to first order either linearly or in terms of the sine and cosine of scaled time from a nearby epoch, which would be a good clear way to present the information. RA & Dec would serve to indicate the pole and the plane of the orbit. For the position, perhaps the distance along the ecliptic from a stated point, and the signed distance from the ecliptic. One might also indicate the stretch of time for which the simple expressions would be good to, say, one degree or 1%; and hope to update them when the mean error reached half that.
I cannot do this myself; I came to the Article to seek such information. 94.30.84.71 ( talk) 13:48, 24 March 2011 (UTC)
RA = 270 + 1.5 * sin(2 pi (Y-2004.39) / 18.6) Dec = 66.2 + 1.5 * cos(2 pi (Y-2004.39) / 18.6)
In the section on lunar standstill, some angular arithmetic is presented that must involve some rounding (23°29′ + 5°9′ or 28°36′) and later (23°28′ − 5°8′ or 18°19′). The first sum would be 28°38′ while the second would be 18°20′. I'm wondering if the (distracting) rounding in this description could be avoided somehow. Or, perhaps it simply reflects an error? Mike Fikes ( talk) 21:48, 5 August 2011 (UTC)
I have read through the entire article and I cannot find a statement of which way the Moon goes around the Earth. Please would someone add this, either in the introduction, or in the section: "Path of Earth and Moon around Sun".
I suggest a sentence in the form: "Viewed from the north, i.e. the direction of the star Polaris, the Moon travels [clockwise/anticlockwise] around the Earth; the Earth travels [clockwise/anticlockwise] around the Sun." Darkman101 ( talk) 17:26, 5 September 2011 (UTC)
This is still too technical for most encyclopedia users, and fails to answer a basic question of observers from the Earth: does the Moon rise in the East or the West? This is not just about the direction of orbit, it is about direction and speed of orbit, relative to the speed of Earth's rotation. A simple "The Moon rises in the East and sets in the West" should suffice (if my assumption is correct). Could someone with the expertise to make the deduction add such a statement in the appropriate place in the article? Thanks. FreeFlow99 ( talk) 11:22, 13 February 2019 (UTC)
I placed a Citation needed template in this section on the claim that the barycenter definition is a criterion. I just went through a search of this for the Double planet article and was unable to find anything on this claim that may be considered a reliable source. I removed the claim (after more than a year) from that article, and I will transfer it from this article to this talk page if a reliable source cannot be found.
One reason the barycenter criterion is not such a good idea is that it is too "time-specific". Since the Moon's orbit is constantly getting a little larger each year, the Earth-Moon barycenter is constantly getting closer to the surface of the Earth. So at some point in the future, when the barycenter is above Earth's surface, then by this criterion the "planet-moon" status will change to "double planet" status. So this criterion or definition is too time-specific and therefore can cause one type of system to turn into another type. – PIE ( CLIMAX ) 16:42, 20 January 2012 (UTC)
This page needs a Java or Flash applet that will show how the Moon, its nodes and apsids all rotate with different periods and in different directions. Prose can only explain so much; a moving model that can be viewed from different angles and different frames is essential here. 24.138.76.31 ( talk) 17:20, 8 June 2013 (UTC)
"some of the Earth's angular (or rotational) momentum is gradually being transferred to the Moon's orbital momentum, and this causes the Moon to slowly recede from Earth at the rate of approximately 38 millimetres per year."
I don't see anything about the change in the length of the month while changing the orbital radius. What is the change in the length of the month? — Preceding unsigned comment added by Reddwarf2956 ( talk • contribs) 04:22, 20 September 2013 (UTC)
The equations which are said to be the basis of the image in the article are not accurate. The image should be shown as accurately as possible in an encyclopedia article. I have written a python program to display the image of the orbit of the Earth and Moon together. This program uses the correct values for the masses, distances, velocities and acceleration according to Newton's law of gravity and therefore shows a true representation of the path of the Earth and Moon together. It does consider the Earth-Moon-Sun as a three-body system and so disregards the gravitational effects of the other planets. This program can be found at http://pastebin.com/NEpwDQxs It requires python 2 or 3 with numpy and matplotlib. Give it time to run. It takes about 26 seconds on my machine. The image of a portion of the earth moon orbit is here http://ctrlv.in/240322 The green curve is the earth orbit and the blue curve is the moon orbit. I would like to replace the image in the article with this image together with an explanation of the equations used to calculate it. I am uncertain how to do this. If someone agrees that this is a worthwhile addition and would like to help put it in, please let me know here.
B A Andersen ( talk) 13:46, 22 September 2013 (UTC)
There is said: "The Moon crosses the same node every 27.2122 days" (the draconic month) There should be said, that it is an average value, where actual time distances between ascending node passages (relative to dynamic ecliptic plane) are currently (this year) in range 27.05 - 27.36 days (the difference is over 7 hours), varying on a sinusoide with 173.3 day period, as detected from NASA/JPL ephemerides DE422. Similar variability (173 day sinusoide) shows the angle between angular momentum vector (orbit axis) of Moon orbit relative to Earth and of angular momentum vector of EMB orbit relative to Sun (on range 5.0328° - 5.30428°). The angular frequency of rotation of a vector from EMB to Moon Ascending Node ranges from 1.6e-5° to 3.21° per 27 days (the low bound could be probably an artifact of discrete position of ascending node calculation? But probably it is not...). I found no mention of the variability of Moon precession here...?! There should be at least the word average draconic month... P.A.Semi — Preceding unsigned comment added by 79.98.159.114 ( talk) 22:45, 18 October 2013 (UTC)
The article says, The sidereal month is the time it takes to make one complete orbit of the earth with respect to the fixed stars, it is about 27.32 days
and later The time between two successive passes of the same ecliptic longitude is called the tropical month. The latter three periods are slightly different from the sidereal month
The sidereal month and the tropical month both refer to one revolution in ecliptic longitude, and in both cases use the rate of change of the mean longitude at an instant. The difference is that the sidereal month refers to a fixed equinox, the tropical year to the equinox of date. Usually the instant and, in the first case date of fixed equinox, J2000.
Simon et al. have 1732559343.736 arcseconds per Julian century. [1]For the J2000 equinox. There being 36525 days in a Julian century and 1296000 arcseconds per revolution, we get 27.32166155 days. Same thing the article gives for the sidereal month.
The same calculation for the mean elements of date agrees perfectly with the tropical month. And it has nothing to do with the vernal equinox. Saros136 ( talk) 08:54, 12 August 2014 (UTC)
I am new to wikipedia and I added a diagram I thought would be helpful. However, I think I have messed up the formmating on the TOC and table at the beginning of this page. Can someone please fix it and let me know what I can do in the future to avoid this? Thank you! -Peter Psobchak ( talk) 23:00, 3 October 2014 (UTC)
Thanks for the input and for helping me on the formatting. I will go ahead and update that spelling error and put in an updated version of the diagram. As for the sourcing, I used the angular data available on this page, and cross-checked it against data from NASA Jet Propulsion Laboratory and they both matched up. I was just trying to illustrate the numbers available on this page in a way that was easier to understand. I will need to look into how I cite sources. Psobchak ( talk) 13:45, 6 October 2014 (UTC)
I replaced the above diagram with this more illustrated version from NASA. It shows all figures except for the angle between the ecliptic and the lunar equator (1.54 degree). Hope that's not too frustrating to the author of the original image. Rfassbind – talk 00:17, 22 August 2015 (UTC)
I would argue that my original image is less cluttered and is easier to read, I am not sure that the new image adds much more to the conversation other than a graphical depiction of the earth and the moon. I find it to be a bit harder to read. I am open to others suggestions on this subject. Psobchak ( talk) 21:26, 12 January 2016 (UTC)
Since the NASA image is now posted twice in this article, I am adding back in the original diagram that I made so that we have the best of both worlds. Additionally, it appears other agree that my diagram contains some good information, I have updated it to fix some spelling errors as well. Again, I am open to feedback on this being the right decision. Psobchak ( talk) 19:05, 3 October 2017 (UTC)
References
Is this a typo? 74.72.169.238 ( talk) 21:52, 19 November 2014 (UTC)
Article is written with Km all over it. Where I live, we work with miles, inperial measurements. I'm struggling with this article because the Km does not quantify the distances. The article and associated articles need updating to show both measurement systems. — Preceding unsigned comment added by 217.35.255.84 ( talk) 12:34, 17 October 2016 (UTC)
All the content pertaining the Tidal rhythmites has no references whithin and they had to be seen on
Tidal acceleration
The citation is Williams, G. "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics 38, 37 (2000).
The contents on the Earth's paleorotation and distance to the Moon is contradicted in a posterior document [1] consulted here Citing from the abstract: "We have shown that analysis of ancient tidal rhythmite may help us to estimate the palaeolunar orbital periods in terms of lunar days/month accurately. Determination of absolute Earth–Moon distances and Earth’s palaeorotational parameters in the distant geological past from tidal rhythmite, however, is ambiguous because of the difficulties in determining the absolute length of the ancient lunar sidereal month." (my bold)
The same concern about the contents and references should be addressed in the Tidal acceleration page.
The page Rhythmite#Tidal_rhythmites is correct because there is no mention of this outdated and erroneous content.
Because I'm not used to edit WP I ask a more experient editor to proceed with the corrections.
62.169.67.133 ( talk) 00:47, 4 November 2016 (UTC)
References
Under "Elliptic shape", the phrase "Julian day 2000" might be a mistake. It might be "Epoch 2000".
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Can someone please add this info about the orbit of the Moon and the Earth's atmosphere? link: [4]. Thank you. -- Miaow 15:10, 26 February 2019 (UTC)
"Semi-major axis[1] 384,748 km (239,071 mi)[2]
Inverse sine parallax[5] 384,400 km (238,900 mi)"
The Semi-major and an 'Inverse sine parallax' is just the same number = 384400 !
And the number: 384,748 km is a hypothetical semi-major axis only; because for the isolated/idealised case of Moon-Earth without any perturbations (mainly of the Sun).
Simply: T = 2pi (a^3/G(M+m))^0.5 = 27.322 days, for a = 384748 km.
Under "Properties" and "Elliptic shape", the phrase "(Julian day 2000)" might be a mistake. — Preceding unsigned comment added by 2A00:23C4:7C87:4F00:A90D:559:F0F0:6602 ( talk) 12:50, 12 August 2020 (UTC)
This diagram claim to be to scale but clearly isn't. For example the earth is ~3.6 times bigger than the moon, in the diagram it's ~2 time bigger. The orbit size compared to the earth size is also wrong. For whatever reason Wikipedia won't let me upload an image with the correct sizes. — Preceding unsigned comment added by Lebesnec ( talk • contribs) 13:25, 30 April 2021 (UTC)
I wonder if anyone can confirm if this research is accurate - I can't find online copies of the obscure citations in fn.27 - On the curve of the Moon’s orbit: A brisk debate between gentlemen, the Trajectorium Lunare and after:
https://www.academia.edu/13219527/On_the_curve_of_the_Moons_orbit_a_brisk_debate_between_gentleman_the_Trajectorium_Lunare_and_after?auto=download
"The final steps towards a mathematical proof of the question were taken in 1761. In a short article, comprising just two pages of textual argument and one diagram the proof was provide[d] by ‘S. Reader, Mathematical’. The article appeared in the January 1761 issue of the somewhat eccentric journal Martin’s Miscellaneous Correspondence.(27) ... No specific reason is given for the timing of the publication, but Benjamin Martin (the Editor) provides the following introduction, ‘I was favoured with the following Theory, by an ingenious and learned Friend at Wareham, some Years ago’. The article is with little doubt due to the Reverend Simon Reader (? – c. 1794), who was well-known at that time as a Dissenting Minister, preaching at Wareham, in Dorset. Apparently, therefore, the article and proof were produced some time prior to 1761, but the exact date remains unclear. Reader provides no references or historical con-text within his article, and simply sets out to prove the introductory statement that: ‘A Demonstration that the Moon passes, at the Time of Conjunction; further from the Sun, than a right Line, drawn betwixt two of its Places, taken, one before and the other after Conjunction, and equidistant from I’’. The Proof is entirely geometrical, and having es-tablished the correctness of the statement, a corollary then asserts that the Moon’s path must be concave to the Sun. Reader’s proof is similar in outline to that provided by John Badder in January of 1743, but rather than relying upon approximate numerical calculations Reader develops a full analytic argument... The same obscurity has additionally befallen the Reverend Simon Reader, who apparently provided the first mathematical proof that the Moon’s path must always be concave towards the Sun. Indeed, the proof of the concavity of the Moon’s path, if even stated with an astronomy text, is invariably taken as being in the ‘public domain’ with no original authorship being recognized." [fn.27: Martin’s Miscellaneous Correspondence, Vol. 4, p. 591, January 1761. There is little biographical data on Simon Reader. According to the memoir of the Reverend W. Hordle (The Evangelical Magazine and Missionary Chronicle, 28 (1850), p. 628 ‘he ran a boarding school and taught Latin, Greek, geography, the use of globes and astronomy’. Reader was educated under Rev. Dr Philip Doddridge (1702-1751) – a leading English Nonconformist minister - and is described as being, ‘a man of extensive learning’ in The Critical Review, Or, Annals of Literature for November, 1795 (p. 319).] Shtove ( talk) 20:02, 16 May 2021 (UTC)
According to this section, libration in longitude is maximal at apogee and perigee. This should be rate of libration, since these are the points where rotational angular speed and orbital angular speed differ most - the amplitude is surely zero at these points. I would edit it myself but am struggling with calculation of the points on the orbit where the angle of libration is maximal - this is where the rate is zero, which is when orbital angular speed is equal to mean orbital angular speed. Or have I lost my marbles?
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Mathglot (
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03:00, 14 October 2022 (UTC)
An image caption in section History of observations and measurement now reads, "The apparent trajectory of the Moon in the sky seen from Earth each night is like a wide ellipse, ... ". Isn't it very close to a great circle on the celestial sphere, at most 1°1′32″ off? The difference is too small to be observed without instrumentation, so why call it an ellipse? -- Lambiam 13:49, 28 June 2023 (UTC)
In effect, this means that the " tropical year" on the Moon is only 347 days long. This is called the draconic year or eclipse year.
Is that so? It's not obvious to me that the precession of the Moon's rotation axis should match that of its orbital plane. —Tamfang ( talk) 18:07, 10 April 2024 (UTC)