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

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
--
Norman Lynagh
Chalfont St Giles, Buckinghamshire
85m a.s.l.
(remove "thisbit" twice to e-mail)

In article ,
Joe Egginton writes:
Why is it, that the phase of the Moon is the same all over the planet?

The moon is about 240,000 miles away. Compared to that, the Earth's
diameter of around 8,000 miles is not very significant. In other words,
everyone on Earth is viewing the moon from approximately the same
direction.
--
John Hall
"It is a very sad thing that nowadays there is so little useless
information."
Oscar Wilde (1854-1900)

Norman wrote:
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

I think Norman was trying to say that the difference in distance between
two places on the earth is small compared to the distance between Earth
and the Moon.

Therefore, although there will be a difference in moon phase when viewed
from two different places on Earth, it's so small as to be negligible.

HTH

Neil

Neil wrote:


Norman wrote:
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

I think Norman was trying to say that the difference in distance between
two places on the earth is small compared to the distance between Earth
and the Moon.

Therefore, although there will be a difference in moon phase when viewed
from two different places on Earth, it's so small as to be negligible.

HTH

Neil


Thanks for all your replies, especially Norman.

--
Joe Egginton
Wolverhampton
175m asl