Joe Egginton wrote:

Why is it, that the phase of the Moon is the same all over the planet?


It's because the moon take about a month to orbit the earth while it
takes only 24 hours for the earth's rotation to complete one complete
revolution.

Imagine the situation where the crescent moon is due south of your
location one night with 20 percent of the disc illuminated. The
following night, if the moon is waxing, there will be a larger
percentage illuminated. I'm not sure exactly how much it increases in
one night but let's assume 26 percent is illuminated when the moon is
due south of you on the second night. Halfway in time between your two
due south sightings someone in the northern hemishphere at longitude
180 deg would see the moon due south with 23 percent of the disc
illuminated. So it's not exactly the same phase. It is continually
progressing. The percentage of the moon's disc illuminated when it is
due south of, say, Berlin will not be exactly the same as the
percentage illuminated when it's due south of, say, London on the same
night but the difference would be very small.

Norman
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Norman Lynagh
Chalfont St Giles, Buckinghamshire
85m a.s.l.
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