# Significance of equal Sun and Moon apparent sizes?

1. Jan 9, 2004

### Loren Booda

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)?

2. Jan 9, 2004

### mathman

I believe its principal effect has been on mythology. As far as the physics of the earth, unlikely.

3. Jan 9, 2004

### Nereid

Staff Emeritus
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?

4. Jan 9, 2004

### Jimmy

Last edited: Jan 10, 2004
5. Jan 10, 2004

### Jimmy

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.

6. Jan 16, 2004

### Phobos

Staff Emeritus
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....