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

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In: Physics

Answer 1

The Moon’s orbit (like all orbits) isn’t perfectly circular. It has a point in its orbit where it makes its closest approach to Earth (perigee), and one where it’s as far away as it gets (apogee). When the Moon is near apogee during a solar eclipse, it doesn’t completely cover the Sun’s disk. You can still see a bright ring of sun around the dark disk of the Moon. This is called an annular eclipse. About 60% of solar eclipses are annular. This percentage will increase as the Moon gets further away from the Earth. Eventually there will only be annular eclipses.