Is the plane in which Moon orbits around earth, inclined with respect to earth's equatorial plane? If yes, is it constant or does it change with time? If it changes, how much time does it take to make a complete circle around earth?
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1$\begingroup$ en.wikipedia.org/wiki/Orbit_of_the_Moon $\endgroup$– planetmakerSep 12, 2022 at 12:11
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5$\begingroup$ I’m voting to close this question because there is no evidence that OP has done any prior research for this question. The Wikipedia article has clearly explained the topic. $\endgroup$– Nilay GhoshSep 12, 2022 at 12:20
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2$\begingroup$ voting to leave open because lack of prior research is not a close reason. The new and increasingly popular "close for insufficient research" close reason, are we headed in the wrong direction here? Is there a way to reduce? $\endgroup$– uhohSep 12, 2022 at 22:08
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2$\begingroup$ @uhoh: Thanks for your support. The purpose of asking a question is to get answers quickly and to the point. (Though it may sound selfish "shortcut"). Doing research is certainly helpful, but it requires lot of time, and perhaps some amount of interpretation. My experience is that sometimes we have to read 1000 pages (for example), to find an indirect answer in 23rd line on page no. 783 of the thousand pages. JUST FYI ... Apollo 11 crew did depend on knowledge gained by earlier space flight crew. They did not repeat the tasks done earlier. Thanks. $\endgroup$– NiranjanSep 13, 2022 at 8:09
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2$\begingroup$ @Uhoh: I accept your response. I agree this time I did not do any homework before asking the question. Without any intention to offend, I think, if sufficient amount of Net surfing/homework on Wiki etc is done, one would get the answer anyway, because after all you or anyone who knows the answer has sourced it from some article / paper / site etc. unless its his own experience (such as that in case of astronauts). In such a case, there is no need to "ASK" a question on this forum. Despite this, I do agree that I should have tried to get some knowledge beforehand. Sorry for that. Will improve. $\endgroup$– NiranjanSep 14, 2022 at 7:41
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1 Answer
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Indeed, the moon's orbital plane is inclined with respect to the earth's equatorial plane, and this inclination changes over time: the angle between both planes varies between 28°36′ and 18°20' with a period of approximately 18.6 years.
This is the combination of the 23°27′ inclination of Earth's equatorial plane with respect to the ecliptic (precession period ~26000 years), and the 5°09' inclination of the Moon's orbit with respect to the ecliptic (precession period ~18.6 years).
Since the precession period of Earth's equatorial plane can be considered negligible compared to that of the Moon's orbital plane, we can just say that the angle between the Moon's orbital plane and Earth's equatorial plane changes with a period of approximately 18.6 years.
You can find more find more information on this topic in Wikipedia's Orbit of the Moon; Inclination to the equator and lunar standstill.
Above: Lunar orbit and orientation with respect to the Ecliptic, showing the values of all relevant angles. (source)
Below: The two extremes, referred to as major and minor Lunar standstill. (source)
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2$\begingroup$ Excellent answer, +1. I already had these drawings in my now-deleted answer so I just copy/pasted them here for the benefit of future readers. Feel free to edit further. $\endgroup$– uhohSep 13, 2022 at 22:39
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2$\begingroup$ @OrOrg: Thanks for the excellent answer. Brings about a lot of clarity. One supplementary question if you don't mind. I understand (may be I am wrong) that the earth's axis of rotation (which is in itself inclined - or "obliquity" by 23.44 degrees), is also not stable, but "VOBBLING" around an imaginary vertical axis. If this is true, earth's equatorial plane will also change its position. In such a case, what happens to the angle of Moon's plane of orbit? Does it remain in sync with equatorial plane, or is it independent? $\endgroup$– NiranjanSep 14, 2022 at 7:31
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2$\begingroup$ @Niranjan Everything you say is correct. The "wobbling" (called 'precession') of the Earth's axis of rotation is the 26000 year cycle. The Moon's plane of orbit also precesses around this same imaginary vertical axis, which is the 18.6 years cycle. However, the Moon's plane of orbit and the Earth's equatorial plane are (at least to very good approximation) independent of each other. $\endgroup$– OrOrgSep 14, 2022 at 7:53
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2$\begingroup$ @Niranjan See iers.org/IERS/EN/Science/EarthRotation/EarthRotation.html for some info on the irregularities of the Earth's motion. $\endgroup$– PM 2RingSep 14, 2022 at 22:59
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