As the moon circles the Earth, it doesn¡¯t give off light of its own. It shines by reflecting light from the Sun.
That is why the Moon gradually seems to change shape in the sky.
We see only the part of the Moon that is facing the Sun!
The side of the Moon that faces the Sun is lit up.
When the Earth is between the Sun and the Moon, we see all of the daylight side, and we say that the Moon is full.
As the Moon swings around the Earth, we see less of the daylight side and more of the dark side.
We say that the Moon is waning.
After a while, all we can see is a thin crescent.
Finally that disappears, too.
When the Moon is between the Sun and the Earth, we can see none of the daylight side.
The dark side is turned towards us, and we say that the Moon is new.
As the Moon continues its trip around the Earth, its daylight side and crescent shape come back into view.
It grows and grows? people call this waxing? until it gets back to its starting point behind the Earth.
Then we see the full Moon again.