Page:Astronomy for Everybody.djvu/145

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MOON'S REVOLUTION AND PHASES
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from one new moon to another is twenty-nine days thirteen hours. The difference arises from the earth's motion around the sun; or, which amounts to the same thing, the apparent motion of the sun along the ecliptic. To

Fig. 19.—Revolution of the Moon Round the Earth.

show this, let AC be a small arc of the earth's orbit around the sun. Suppose that at a certain time the earth is at the point E, and the moon at the point M, between the earth and the sun. At the end of twenty-seven days eight hours the earth will have moved from E to F.

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