Why does the moon rise and set 50 minutes later each night?
a. the moon s rotation is longer than earth s revolution.
b. the moon s revolution is longer than earth

The moon makes one full rotation around the earth every month (29.53 days). This means that it makes one 360 degree rotation every ~30 days, which is 12 degrees of movement per day. 

Since the earth rotates once every day, so it makes one 360 degree rotation every 24 hours.

To determine how many 'hours' later 12 degrees is, do: 12 degrees / 360 degrees * 24 hours(in a day) = .8 hours, which if you multiply by 60 you get 48 minutes. 

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