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If you ever look up at the moon at night sky -- say, before you go to bed -- you've probably
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noticed that, as the days and weeks go by, the moon looks like it's changing shape.
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Some nights, it's a little sliver.
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And some nights, a few weeks later, it's a big bright circle!
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Well, the moon doesn't actually change shape.
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But our view of it does change.
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Why?
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Well, the moon, just like the Earth, has a day side and a night side -- a part that's
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facing the sun, and a part that's not.
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So when we see a little sliver of bright moon, we're seeing a little part of the moon that's
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facing the sun, while the rest of the side that's facing us, is dark.
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And the size and shape of that little sliver of lit-up moon changes, because the moon orbits,
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or moves around, Earth.
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It takes the moon about one month to make a one full orbit around the Earth.
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And as it moves around our planet, the day-time side of the moon -- the side that's lit
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up from the sun -- is facing in different directions, as we see it from Earth.
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This means that, every night, we get a slightly different view of the moon!
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And during its month-long trip in orbit around the Earth, the bright part of the moon appears
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to grow, and then shrink, from right to left!
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The different shapes that we see, of the lit-up part of the moon, are called phases.
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And there are eight phases of the moon.
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The first phase is the new moon.
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This is when the nighttime side of the moon -- the side that's facing away from the
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sun -- is what we can see from Earth.
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The moon is still up there!
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But because its dark side is facing us, we can't see it during the new moon phase!
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The next phase is called the crescent phase.
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This is when the moon looks like a little sliver, kind of like the tip of your fingernail!
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After the crescent comes the quarter moon -- this when the moon looks like half-circle!
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The next phase is called gibbous.
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A gibbous moon is when it's missing just a little sliver of light, and it's almost
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full!
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And that's what's next!
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The moon is at its brightest at the full moon.
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That's when the fully-lit side of the moon is facing us, so we see a big, bright circle.
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But we're only halfway through our phases!
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After the full moon, the lit-up part of the moon appears to shrink.
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And just like how it grew from right to left, the sunny side of the moon will shrink from
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right to left too!
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So, after the moon is full, it starts to shrink back down to a gibbous moon.
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But this time, you'll notice that the left side is shining bright instead of the right!
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And after the gibbous phase, the moon will look like half circle again, when it reaches
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the quarter moon phase again.
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And then after a few days, it shrinks down to a little sliver again ... the second crescent
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moon.
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After that, the tiny sliver shrinks all the way down until the lit-up side of the moon
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can't be seen at all.
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Now, the moon is a new moon again.
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It's the same old moon!
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But it's gone through a month-long cycle of phases, and is ready to start all over
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again.
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Like I said, it takes a month for the moon to go through all eight phases.
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And in fact, our word “month” comes from the word “moon,” because it takes a month
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for the moon to go from new moon, through all of its phases, and back to new moon again.
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So, tonight, before you go to bed, take a look out the window.
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If the sky is clear, can you see the moon?
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If you can, what phase is it in?k
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Is the bright part on the right side or the left side?
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Keep an eye on it as the days go by, and watch how the moon looks like it's changing shape.
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You can even make drawings to keep track of how it changes from day to day.
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Now you know that the moon itself doesn't really change shape.
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We just see different amounts of the sunny side of the moon, as it makes its monthly
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trip around the Earth.
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Thanks for joining us today!
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We love getting questions here at the Fort!
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So if you have one...ask a grownup to help you leave a comment down below, or to send
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us an email to kids@SciShow.com!
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And we'll see you next time!
