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Comment by GEBBL | Hacker News Reader

Does the moon take a lot of impacts that would have been destined for earth?

Most of the stuff that leaves a small crater on the moon would burn up in Earth's atmosphere long before it hits the ground.

Random Factoid: it's extremely rare but the reason why the moon appears the same size as the sun is that the sun is 400x wider than the moon, but also 400x farther from the earth than the moon is.

Our moon holds so many mysteries. Just the very fact that such a large object can be so close in proximity to us while also orbiting is mind boggling.

https://astronomy.com/magazine/ask-astro/2000/10/why-is-the-...

Random other factoid: The diameter of the Moon is less than the width of Australia at its widest part.

I’ve always found this to be a curious coincidence, that the Sun’s corona remains visible during total solar eclipses because the Moon blocks out the Sun just so.

But the really fun part is described in the link above:

> Tidal interactions cause the Moon to spiral about one inch per year away from Earth. In the distant past, the Moon was close enough to Earth so that it could block the Sun's entire disk and then some. Our prehuman ancestors would not have witnessed the beautiful coronal displays that we now enjoy. And about 50 million years from now, the Moon will be far enough away so that our descendants will only see annular eclipses.

That seems to be actually be true, not a factoid?

American heritage dictionary:

factoid

făk′toid

noun

1. A piece of unverified or inaccurate information that is presented in the press as factual, often as part of a publicity effort, and that is then accepted as true because of frequent repetition.

2. A brief, somewhat interesting fact.

3. An inaccurate statement or statistic believed to be true because of broad repetition, especially if cited in the media.

I assume the definition used here is #2. I’m actually surprised by 1 and 3. I have never heard it used in that context and it’s strange that one word would have 2 fairly contradictory interpretations.

That is interesting! I've never come across the second definition before. Wikipedia suggests that usage become common following CNN misusing the original Norman Mailer meaning during broadcasts in the eighties.

https://en.wikipedia.org/wiki/Factoid

Now that is an interesting factoid!

I have the same question, if anyone knows the answer it'd be awesome.

I mean, sure, simply by virtue of the moon's being there, it sort of fends some stuff off like a fence.

But beyond that, is its gravitational pull adequate to affect trajectories?

If so, wouldn't earth's trump it? (Although the inverse square here may play a big part, but that would also make me more inclined to disregard the moon's gravity pull as assisting in any protection it otherwise naturally affords.)

Edit: clarified (?) thought

I think the effect of the moon is not so much "catching" things as it is perturbing orbits near earth such that things either crash into earth or moon or get flung away.

Without the moon we might have a lot more stuff in solar orbits that overlap earths orbit.

I expect this could be explained better (and I may well be totally wrong).

It’s really more that the moon has no atmosphere. A shooting star on Earth would be a crater on the moon.

Ackshually, the moon has a very thin atmosphere, primarily composed of neon, helium and hydrogen.

Not enough to matter for most purposes.

The first requirement for a piece of space junk to hit the moon is to be on an orbit that will cross the moon's. Most space junk is left over from launching things into earth orbit (geostationary or lower), and so will not be going fast enough.

That would be Jupiter and Saturn. For this instance, it’s other way around.

Yeah, Jupiter is basically a giant hoover of the solar system - apparently without it Earth would be constantly getting hit by outer space junk.

About as much as the percentage of the sky it covers, I assume?

This is correct, and it's not much, the Moon covers only 1/210000th of Earth's sky. https://en.wikipedia.org/wiki/Square_degree

The Moon does take slightly more than that proportion of impacts that would hit Earth, because the distribution of approach vectors of impacting bodies isn't uniform, but clusters around the ecliptic plane, and so does the Moon's orbit. But it's still a small number.

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