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Name: Chuck P.
Status: other
Grade: other
Location: CA
Country: N/A
Date: 6/28/2005
Question:
How much is the average distance between Earth and the moon changing with time? Is the moon getting closer or more distant from Earth?

Replies:
Chuck,

During the Apollo mission, Neil Armstrong placed a series of what are essentially mirrors on the surface of the moon. Earth scientists could then bounce a laser off these reflectors and by analyzing the time it takes for the light to come back (accounting for such things as atmosphere and so on) precise data could be made about the moon's distance, it's spin rate, and how fast it is receding from the Earth. Currently it is receding at about 1.5inches per year.

Btw, the fact that the moon is receding (instead of being pulled in by Earth's gravity) is a strong suggestion that the moon was created during a massive collision.

Greg (Roberto Gregorius)


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