5 ms·
Why the two sides are so different is one of the Moon’s most enduring mysteries. How much can be explained by the earth shielding the moon from impacts to its
by rhplus 4y ago
Why the two sides are so different is one of the Moon’s most enduring mysteries.
How much can be explained by the earth shielding the moon from impacts to its near-side?
- spaetzleesser 4y agoThat’s what I was thinking. Or that the earth gravity would cause tidal forces.
- vikingerik 4y agoNot much. The Earth subtends a width of only 2° in the Moon's sky - it covers only about 1/10000 of the possible approach vectors to the Moon. Think about a lunar eclipse for comparison: the Earth intercepts the Sun-Moon vector for a couple hours every few months, roughly 1/10000 of the time. The Moon is a smaller target (1/4 the diameter, 1/16 the cross section, also 1/81 the mass and gravity), so it gets hit less because of that, but not because of Earth shielding it.
- cperciva 4y agoI don't think that calculation is quite right. An asteroid on a collision course with the moon doesn't need to hit the Earth in order to avoid hitting the moon -- simply coming close to the Earth will alter its course.
- vikingerik 4y agoIt's just as likely that the Earth will perturb an object's course away from the moon as into it. Except if the object hits Earth itself, but the point is that's a pretty small percentage of cases, the Earth occupies only a small portion of the moon's sky.
- cperciva 4y agoAre the probabilities equal? I agree that they're both possible, but I don't have any clear intuition for why they should be the same -- or which would be larger if they're not the same.