gino@voder.UUCP (Gino Bloch) (09/20/84)
>> 1) Is the moon visible above the polar horizons? All the time, or only >> part of the year? >> 2) If it is visible at all, is it seen during the polar six-month "night", >> the six-month "day", part of both, or what? Is it right on the horizon >> when it is visible, or higher? >> Will Martin With reference to 1: I think it's obvious that the moon is not simultaneously *above* both POLAR horizons, though it will be visible simultaneously at a reasonable distance form both poles when the moon is close to the celestial equator. Actually, when the moon is exactly on the equator, atmospheric refraction will make it appear to be just touching the horizon from both poles. If we pump away the atmosphere, this effect will disappear, and both horizons will split the moon. Generally, the moon's visibility is similar to the sun's with these two differences: 1. The moon revolves around the earth monthly; the sun's apparent revolution is a year long (this is with respect to the stars). 2. The moon's orbit is tilted about 5 degrees WRT the sun's apparent orbit, so the moon can appear closer to the horizon than the sun - or even below the horizon - and it can also appear farther from the horizon than the sun - hence visible when the sun isn't (complementing the first half of this sentence). However, the places where the moon's path crosses the sun's revolve (I forget how fast; the time span is of the order of decades, I'd guess), so the times of the month when the moon is higher than the sun change over time. -- Gene E. Bloch (...!nsc!voder!gino)