In reality the moon doesn't change shape at all ,its orbiting the earth at the same time, it is also rotating, and the earth itself is rotating and revolving around the sun, that is why stars move in the sky and why the sun and moon  rise and set in different locations each day. 

the only thing that changes then is not the shape of the moon but the appearance of the reflected side -the part that looks bright to those of us in earth 
we simply see a different angle of the reflected side each day ,minute,hour,week and month. this gives the appearance of a new moon ,full moon when in the fact the moon shape is just the same as it  was before . 
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