# Significance of equal Sun and Moon apparent sizes?

by Loren Booda
Tags: apparent, equal, moon, significance, sizes
 P: 3,394 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)?
 Sci Advisor P: 5,776 I believe its principal effect has been on mythology. As far as the physics of the earth, unlikely.
 PF Patron Sci Advisor Emeritus P: 3,940 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?
P: 616

## 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
 P: 616 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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