The Universe
Yours to Discover
Sky Science
Part 7 - The Phases of the Moon
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7. Recognize that the Moon's phases are regular and predictable, and describe the cycle of its phases.
8. Illustrate the phases of the Moon in drawings and by using improvised models. An improvised model might involve such things as a table lamp and a sponge ball. |
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The Moon goes around the Earth. This motion is called revolution. It takes about a month, for the Moon, to go around the Earth once. The path that the Moon takes as it goes around the Earth is called an orbit. The Moon's orbit is not perfectly circular. The actual shape of the orbit is called an ellipse, which is like a stretched out circle.
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NOTE: The Earth to Moon Distance in this video is Not to Scale
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Please note that the size of the Earth and the Moon in this video are to scale, but the distance between the Earth and the Moon is NOT to scale. The Moon is actually much farther away from the Earth than it appears in this video.
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As the Moon revolves around the Earth each month, we see different amounts of the Moon lit up by the Sun. Sometimes we see one entire side of the Moon lit up, which we call a Full Moon. At other times, we can only see one-half of the side of the Moon that is lit up, which we call a Quarter Moon. Sometimes we see less than half of the side of the Moon that is lit up, and at other times we more than half. There is even a time each month when you can look up into the sky over the course of 24 hours and not see the Moon at all. That's called a New Moon. All of these different "looks" that the Moon has over the course of a month are known as the Phases of the Moon.
In the diagram below, you will notice that the Sun shines on the Earth and on the Moon. It always illuminates half of our planet and half of the Moon. In other words, half the Earth is always experiencing daytime, while the other half is experiencing nighttime. The same is true on the Moon, but because the Moon revolves around the Earth, while it is being illuminated by the Sun, we see different amounts of the illuminated side of the Moon (from here on Earth) over the course of a month. This results in the Moon having some different "looks" over the course of the month and we call these different looks the Phases of the Moon.
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There are 8 Phases of the Moon and below we're going to go through them one by one.
Afterward, there is a video that you may enjoy watching that will hopefully reinforce all this information. Please note that the size of the Earth, Moon, and Sun in this diagram are to scale. Also, the distances between the Earth, Moon, and Sun are not to scale. |
In the diagrams below, you will see the Moon positioned in 8 different locations around the Earth, with each location labelled 1 through 8. At the bottom of each diagram, you will see a corresponding view of the Moon.
New Moon
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In position 1, the side of the Moon that is illuminated is NOT facing Earth and so we can't actually see the Moon. This is called a New Moon and since you can't see it, it appears black in the view located at the bottom of the diagram.
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Waxing Crescent Moon
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In position 2, the side of the Moon that is illuminated is only facing Earth a little bit and so we only see a little bit of the Moon illuminated. This is called a Waxing Crescent Moon and as you can see at the bottom of the diagram, where it is labelled "2" the Moon appears to have a crescent shape.
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First Quarter Moon
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In position 3, we can see (from here on Earth) one-half of the side of the Moon that is illuminated. This is called a First Quarter Moon because at this point, the Moon has travelled one-quarter of the way around the Earth. The Moon appears one-half lit up at this point, as you can see by taking a look at the view of the Moon labelled "3" at the bottom of the diagram.
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Waxing Gibbous Moon
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In position 4, we can see more than half of the illuminated side of the Moon, but we can't see all of it just yet. This is called a Waxing Gibbous Moon and it looks just like what you see in the view of the Moon labelled "4" at the bottom of the diagram.
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Full Moon
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In position 5, the Moon has travelled half-way around the Earth and we see the entire illuminated side of the Moon. This is called a Full Moon and since you can see all of it, it appears white in the view located at the bottom of the diagram.
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Waning Gibbous Moon
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Now the Phases of the Moon repeat, but in reverse. In position 6, we can no longer see the entire illuminated side of the Moon, but we can see a lot of it. This is called a Waning Gibbous Moon and it looks just like what you see in the view of the Moon labelled "6" at the bottom of the diagram. Please notice how it resembles the other Gibbous Moon, the one that is labelled "4" at the bottom of the diagram.
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Third Quarter Moon (Last Quarter Moon)
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In position 7, we can see (from here on Earth) one-half of the side of the Moon that is illuminated. This is called a Third Quarter Moon or a Last Quarter Moon because at this point, the Moon has travelled three-quarters of the way around the Earth or you could say it only has one last-quarter to go before it has completed its trip around the Earth. Please notice how it resembles the other Quarter Moon, the one that is labelled "3" at the bottom of the diagram.
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Waning Crescent Moon
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In position 8, the side of the Moon that is illuminated is only facing Earth a little bit and so we only see a little bit of the Moon illuminated. This is called a Waning Crescent Moon and it looks just like what you see in the view of the Moon labelled "8" at the bottom of the diagram. Please notice how it resembles the other Crescent Moon, the one that is labelled "2" at the bottom of the diagram.
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After the Moon has passed through all 8 phases, the process begins again. So, after position 8, the Moon returns to position 1 and the cycle begins once again. It takes approximately 29.5 days (about one month) for the Moon to complete this cycle.
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Please note that the size of the Earth, Moon, and Sun in this diagram are to scale. Also, the distances between the Earth, Moon, and Sun are not to scale.
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