Why does the moon have phases?
As we watch the moon night after night, it seems to change its shape. These different appearances are called phases.
The moon’s rotation around the earth causes the phases.
The moon gives off no light of its own. It reflects the light from the sun. The sun can light up only one half of the moon at a time.
The phase that we see from the earth at any time depends on how much of the lighted side is turned towards us.
When the moon is between the earth and the sun, its dark side is turned toward the earth. At this time, the moon is almost invisible. It is called the new moon.
A thin crescent appears as we begin to see part of the sunlit side. Each night the crescent gets a little larger. After a week, it is a half moon.
At full moon, the moon has circled far enough for us to see all the sunlit half. As it completes its journey around the earth, the moon again passes through all its phases. – Dick Rogers