Is the moon really moving away from the earth? and where is this write down, in what book or research paper?

This effect is well documented in many journals, books and publications. For one, the “Encyclopedia of the Solar System” (ed. McFadden, Weissman and Johnson. 2nd edition 2007, page 228) states that “The Moon is receding from the Earth, due to tidal interaction, at a rate of 3.74 cm/year.”

You can visualize this effect by recalling some high school physics and the conservation of angular momentum. The Moon causes tides here on Earth, but the Earth is rotating on its axis faster than the Moon is orbiting around the Earth. Thus the “bulge” that is created on the Earth by the tides continually is trying to drag the Moon around faster (through gravitational forces) than it is currently going. So the Moon is acting like an anchor and slowing down the Earth’s rotation, just as the Moon is consequently increasing its orbital speed around the Earth. If it is truly getting faster, conservation of angular momentum tells us that it also has to be getting further away from the Earth at the same time!
Brad Bailey
NLSI Staff Scientist

July 13, 2010

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