Jessi: If you ever look up at the moon at night sky -- say, before you go to bed -- you’ve probably noticed that, as the days and weeks go by, the moon looks like it’s changing shape.

Some nights, it’s a little sliver. And some nights, a few weeks later, it’s a big bright circle! Well, the moon doesn’t actually change shape. But our view of it does. Why?

Well, the moon, just like the Earth, has a day side and a night side -- a part that’s facing the sun, and a part that’s not. So when we see a little sliver of bright moon, we’re seeing a little part of the moon that’s facing the sun, while the rest of the side that’s facing us, is dark. And the size and shape of that little sliver of lit-up moon changes, because the moon orbits, or moves around, Earth.

It takes the moon about one month to make a one full orbit around the Earth. And as it moves around our planet, the day-time side of the moon -- the side that’s lit up from the sun -- is facing in different directions, as we see it from Earth. This means that, every night, we get a slightly different view of the moon!

And during its month-long trip in orbit around the Earth, the bright part of the moon appears to grow, and then shrink, from right to left! The different shapes that we see, of the lit-up part of the moon, are called phases. And there are eight phases of the moon.

The first phase is the new moon. This is when the nighttime side of the moon -- the side that’s facing away from the sun -- is what we can see from Earth. The moon is still up there!

But because its dark side is facing us, we can’t see it during the new moon phase! The next phase is called the crescent phase. This is when the moon looks like a little sliver, kind of like the tip of your fingernail!

After the crescent comes the quarter moon -- this when the moon looks like half-circle! The next phase is called gibbous. A gibbous moon is when it’s missing just a little sliver of light, and it’s almost full!

And that’s what’s next! The moon is at its brightest at the full moon. That’s when the fully-lit side of the moon is facing us, so we see a big, bright circle.

But we’re only halfway through our phases! After the full moon, the lit-up part of the moon appears to shrink. And just like how it grew from right to left, the sunny side of the moon will shrink from right to left too!

So, after the moon is full, it starts to shrink back down to a gibbous moon. But this time, you’ll notice that the left side is shining bright instead of the right! And after the gibbous phase, the moon will look like half circle again, when it reaches the quarter moon phase again.

And then after a few days, it shrinks down to a little sliver again... the second crescent moon. After that, the tiny sliver shrinks all the way down until the lit-up side of the moon can’t be seen at all. Now, the moon is a new moon again.

It’s the same old moon! But it’s gone through a month-long cycle of phases, and is ready to start all over again. Like I said, it takes a month for the moon to go through all eight phases.

And in fact, our word “month” comes from the word “moon,” because it takes a month for the moon to go from new moon, through all of its phases, and back to new moon again. So, tonight, before you go to bed, take a look out the window. If the sky is clear, can you see the moon?

If you can, what phase is it in?k Is the bright part on the right side or the left side? Keep an eye on it as the days go by, and watch how the moon looks like it’s changing shape. You can even make drawings to keep track of how it changes from day to day.

Now you know that the moon itself doesn’t really change shape. We just see different amounts of the sunny side of the moon, as it makes its monthly trip around the Earth. Thanks for joining us today!

We love getting questions here at the Fort! So if you have one...ask a grownup to help you leave a comment down below, or to send us an email to kids@SciShow.com! And we’ll see you next time!