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

It is a coincidence. We just happen to live during the period of time where the angular diameters of the Sun and Moon are, sometimes, nearly equal, giving us the opportunity to view a “total” solar eclipses.

However, not all eclipses are total. The moon’s orbit is an ellipse, aka not perfectly circular, which means that its distance from the Earth varies over time. When it’s farther from Earth, it appears smaller in the sky, and if an eclipse happens when it appears small like this, we called it an Annular Solar Eclipse. In the middle of the event, the sun appears as a solid ring of light with the dark moon right in the middle – not large enough to completely block the sun like during a Total Solar Eclipse.

The moon orbited closer to the Earth in the past, and it will continue to drift further away in the future. Eventually, it will get so far and appear so small that it will never be able to fully block the sun like it can now, so we could still see annular eclipses, but we would never experience a total eclipse again.

We’re pretty lucky that we live during the time when we can! I missed my opportunity to view one back in 2017 due to a job interview. I’ve vowed to not let myself miss the next one.