Significance of equal Sun and Moon apparent sizes?


by Loren Booda
Tags: apparent, equal, moon, significance, sizes
Loren Booda
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#1
Jan9-04, 11:31 AM
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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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mathman
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Jan9-04, 04:55 PM
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I believe its principal effect has been on mythology. As far as the physics of the earth, unlikely.
Nereid
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Jan9-04, 09:42 PM
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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?

Jimmy
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Jan9-04, 11:55 PM
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Significance of equal Sun and Moon apparent sizes?


I found several values for the rate at which the moon is moving away from the earth. 3.8cm/yr seems to be a good approximate value. However, I'm guessing that this rate hasn't been constant over a period of 500 million years or more.

http://www.lpi.usra.edu/expmoon/Apol...ents_LRRR.html
Jimmy
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Jan10-04, 12:25 AM
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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.
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Jan16-04, 12:12 PM
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Originally posted by mathman
I believe its principal effect has been on mythology. As far as the physics of the earth, unlikely.
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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