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Significance of equal Sun and Moon apparent sizes?

  1. Jan 9, 2004 #1
    How has the near equality of the Sun's and Moon's apparent size (as seen from Earth) affected our planetary history (vs transient phenomena like eclipses)?
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  3. Jan 9, 2004 #2


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    I believe its principal effect has been on mythology. As far as the physics of the earth, unlikely.
  4. Jan 9, 2004 #3


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    As the Moon's distance from the Earth has, over our double planet's history, changed quite a lot - and as the Earth's distance from the Sun has been pretty much constant - the apparent near-equality we see today is a curious coincidence in time.

    Anyone got a reference (or want to do a calculation) on how the average angular size of the Moon (as seen from the Earth's surface) has changed in the last 500 million to 3 billion years?
  5. Jan 9, 2004 #4
    Last edited: Jan 10, 2004
  6. Jan 10, 2004 #5
    If we assume that the moon is receding at a constant rate of .038 m/yr, 1 million years ago, the moon was 38,000 meters closer. Compared to it's present distance of 3.84x10^8 m, the moon was closer only by a factor of 1.00009896. If today, the moons average apparent size is only 30 arc minutes, 1 million years ago, it would have subtended an additional .18 arc seconds.

    A billion years ago, it would have been 38 million meters closer. A factor of about 1.1 times closer. It's apparent size would have been larger by about 3 arc minutes.

    These calculations are probably wildly inaccurate in reality.
  7. Jan 16, 2004 #6


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    e.g., ancient astronomer's/astrologer's ability to predict eclipses was a source of political power. Maybe I can come up with some examples, L.B....
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