Long-term Day-length Calculation ``` Name: Mark Status: other Grade: other Country: USA Date: Spring 2013 ``` Question: If the moon moves away from the earth approximately three meters every hundred years, and the earth slows down, is there anyway to figure out how long the day would be in two billion years? Replies: Dear Mark, A very perceptive question. I believe you are correct that the Moon has inched about a meter farther from Earth in the past century. The Earth's primordial day was about 6 hours, and that 620 million years ago, the day was 21.9 hours long. If the rate of slowing remains constant, then in 600 million years from now the day will be about 26 hours long, and incidentally the Moon will be so far from Earth that there will never again be a total eclipse of the Sun; solar eclipses will all be annular. In 2.4 billion years from now the Earth will have a day that is eight hours longer than now, or 32 hours. I am not certain of this, and I doubt I'll be around to experience it! Sincerely David H. Levy Click here to return to the Astronomy Archives

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