I'm in the northern hemisphere, facing north, and notice that the moon is due north (azimuth 0) and is still above the horizon, albeit barely.
Does this mean the moon is necessarily circumpolar (doesn't set), at least for the next few hours?
As the moon moves away from due north, it's altitude/elevation normally increases. However, it's possible that the moon's declination is decreasing so rapidly that the moon's elevation actually decreases, and the moon sets.
Is this possible?
This question is tangentially related to my question "libnova odd behavior for 89.5 degrees north latitude" on Stack Overflow.
EDIT to answer questions: I am facing true north. I am referring to the Earth's true moon, but not necessarily in any given time frame. In other words, if something like this happens 10,000 years from now, that's fine.
EDIT: OK, I believe the moon CAN set even if it's up when due north. Example:
You are at latitude 89.5N
The moon's declination when due north is +0.5N. This means the moon grazes the horizon when due north.
If the moon's declination were constant, it's highest elevation for the day would be 1 degree.
Since the moon's declination can change more than one degree per day (average of 1.5 degrees/day), it's quite possible for the moon's declination to go below -0.5N, at which point it would have set (it will actually set before this point unless it happens to reach due south).
In theory, this could happen with any object whose declination changes, provide you're close enough to the North Pole.
I'll leave this update open for critiques.
EDIT: Actually, this whole question is just asking whether the midnight sun/moon can set at any position other than due north, which is fairly obviously true. Reasoning: once the moon/sun finally sets not due north, it was obviously still up the last time it was due north.