The moon takes about a month to orbit the
earth, and therefore, that is how long it takes
to go through its phases from a light crescent
that waxes (light part grows) until it reaches a
full moon, and then wanes (light part shrinks)
back to a thin crescent and then a new moon (only
the dark side of the moon faces from earth, making
it invisible at night).
When you see the moon moving across the sky in a
single night – from its rising to its setting –
you are catching the moon in just a very short
window of time (a few hours) during this process
that takes a full month! So the change of
“shape” of the moon is basically imperceptible in
the short time between its rising and setting in a
single night. The moon’s “shape” largely looks
the same from moonrise to moonset each night and
the change can be observed not within a single
night, but over multiple nights.
I hope that answered you question adequately!
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