Exercise:

The Moon was New on December 25th, 2000.
At St.Andrews, on January 1st 2001,
the Sun crossed the meridian at 12:15.
At what time did the Moon cross the meridian?

On January 1st,
7 days had elapsed since New Moon
(the Moon was "7 days old").
So the Moon was lagging the Sun by 7x48.8 minutes = 5h42m.

So it would cross the meridian at 12:15 + 5h42m = 17:57.

In fact it crossed the meridian at 17:24,
so our calculation is in error by 33 minutes.
The error is due to:
(a) not knowing the exact time of New Moon on December 25th
(b) the Moon's motion not being constant.

Back to "The Moon".