The Moon can block the Sun completely during a solar eclipse because the Sun is far, far away. Is it then pure coincidence that the Moon almost completely fits the Sun’s outline, or could we’ve had solar eclipses with a much smaller Moon, thus blocking the sun only very partially?

Question

Title.

In: Physics

Answer 1

Yes, it is a coincidence. The Sun is roughly 400 times the size of the Moon, and roughly 400 times further away from Earth than the Moon is. So it happens to be about the same size in the sky.

If you look at other moons of the solar system, this is not the case, and so you would not get these near-perfect eclipses. For example, the largest moons of Jupiter all have a larger apparent size (when seen from Jupiter) than the Sun does, and so it wouldn’t line up so nicely, they’d completely block the sun. Other moons are smaller than the apparent size of the sun and would instead transit the Sun without eclipsing it.

As far as I know there’s no particular benefit to having this coincidence, it’s just nice.