Why does the moon seem to change shape every month? And why are their nights when the moon doesn’t come up at all? The answer to all of these questions can be explained by understanding 2 things (Phases of the Moon):
1. The moon orbits around the earth. This happens nearly every 28 days (27.32 days to be precise!).
2. We see the moon only because it reflects sunlight back to earth. The moon is not a light-producing star like the sun. It is a giant rock and we need sunlight to see it.
As the moon orbits around the earth every 28 days, part of it is always hit by the sun’s light, just like it’s always day time somewhere on earth even if it is dark where you are! However, when the moon is between the earth and the sun, its back is lit up but its front is facing us in shadow, so we can’t see it! This is called a new moon.
As the moon moves further around, we begin to see a small bit of its lit-up side and we call this a waxing crescent moon. When the moon is 90 degrees away from the line of the earth and the sun, we can see half of it lit up and we call it a half moon. As it moves further along, we call it gibbous, as we can see more of the moon every day (waxing), and when the moon is roughly behind the earth, we can see all of the sun’s light reflecting back on it and we call it full.
Then the moon starts coming around the other way and we can see less and less of it every day (waning).
We’ll see a waning gibbous moon, a half moon, a crescent, and finally back to seeing no moon at all (phases of the moon)!