- Do either of the standstills (N/S) coincide with full/new moon?
- If yes - what is the relationship?
- If no - what factors impact the relationship between the two?
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1 Answer
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Do lunar standstills (North or South) coincide with full Moon/new Moon/any phase? No.
A standstill occurs when the Moon reaches the northern most declination (or southern) in its orbit. That occurs approximately every 27.3 days.
The phase is related to the position of the Moon relative to the Sun. Since the Sun appears to be moving in the sky, the time from new Moon to new Moon is approximately every 29.5 days.
Because the two periods (27.3 and 29.5 days) are different and not a simple ratio (such as 2 to 1), there is no direct correlation between the standstills and the Moon's phase.
answered Oct 31, 2022 at 17:21
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1$\begingroup$ Don't standstills occur twice approx every 27.3 days? $\endgroup$– Connor Garcia ♦Commented Oct 31, 2022 at 18:09
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1$\begingroup$ @ConnorGarcia Yes, the northern standstill occurs every 27.3 days, and the southern standstill occurs every 27.3 days. They are offset by approximately two weeks. (I'm not sure if it is exactly half the sidereal period!) $\endgroup$ Commented Oct 31, 2022 at 19:15
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1$\begingroup$ @JohnHoltz: they would be exactly half if the orbit were circular and not perturbed by the sun. Ignoring the sun, the half that has the perigee in it will be faster. The sun messes it up by making the half traveling toward the sun faster than the half traveling away. I don't know what dominates. $\endgroup$ Commented Oct 31, 2022 at 23:57
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1$\begingroup$ @JohnHoltz That piqued my interest so I've asked a follow-up question How do times of lunar standstills vary over time? If we folded them back into a lunar month plot, would they have "prograde and retrograde motion"? $\endgroup$– uhohCommented Nov 1, 2022 at 2:20
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