Why does the moon have phases?

+53 votes
asked May 12, 2015 in Science by XIAORONG (880 points)
Most nights of the week I sit outside on my porch and enjoy looking at the night sky with my dog, my boyfriend, friends or whoever will share a relaxing evening with me! It’s so refreshing after a long day. The phases of the moon really make a difference how much light there is, and I’ve always wondered why the moon changes at all. Why does the moon have phases and why do they cycle every month?

2 Answers

+25 votes
answered May 16, 2015 by Shana (840 points)
The moon has different phases because of the light we see reflecting off it, and as it moves we see different angles. The moon takes about 30 days to revolve around the Earth, so the cycles we see run the course of a month. There’s always a consistency to this because the moon always takes the same amount of time to orbit. That’s why we’re able to predict and track the cycles as well because we’re already able to track the moon’s revolutions. People have been able to do this for a very long time, starting with our first ancestors. The famous almanacs that used to be really popular with farmers would always have information about important phases of the moon and the dates they could be seen.
+2 votes
answered May 18, 2015 by Lynda (620 points)
edited Sep 10, 2015 by Kris
So why does the moon have phases? Depending on the alignment of the moon, Earth, and sun, we’re able to see different amounts of the surface of the moon called phases. The reason why we can see these parts of the moon is because we’re looking at the reflected sunlight on the moon’s surface. A new moon happens when the moon is directly between the Earth and the sun. The surface getting all of the sun’s light is the face of the moon on the opposite side from Earth, so it appears as nothing in the sky to us. On the other hand, a full moon happens when the Earth is directly between the moon and the sun. We can see the full surface of the moon because all of the sunlight rays are directed at the side closest to Earth. One of the really interesting things about the part of the moon we see is that the way the moon revolves around the Earth makes it so that we only ever see the same side of the moon. No one looking at the moon from Earth will ever be able to see the other side of the moon.
commented May 21, 2015 by Waldemara (380 points)
Oh, I understand why does the moon have phases now, but it’s so sad that we can’t see the other side of the moon from earth ;(
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