Phases of the moon.
As the moon orbits the earth
We see the different phases of the moon.
This is because the moon is iluminated differently as it orbits us.
Lets start with a new moon
This is a difficult phase to see as it appears close to the sun.
as it moves we see it as a waxing cresent
after that it becomes the
first quater, when the moon makes a 90' angle between the earth and sun
on to waxing gibbous
and then the full moon - when the moon is the opposite side to the sun
then the waning gibbous
third quarter moon.
Waning cressent.
And back to a new moon
This takes a period of about 28 days.