Annular Eclipse


There was an eclipse today in some parts of the world. Not here though. This was an annular eclipse, where the moon doesn’t fully cover the sun and leaves a ring of sun shining behind the moon.

So why does this happen. In normal eclipses the moon appears to be the same size as the sun so its completely covered. That is because the moon is something like 40 times smaller than the sun, but also 40 times closer to us. So they have the same apparent size in the sky. But with an annular eclipse the Sun can be slightly closer or the moon slightly father away. Why? Because the Earth rotates round the Sun in an ellipse, which is an oval with two focal points. The sun sits on one focus, but the Earth orbits around both. That means sometimes it is further away from the sun and sometimes closer Then it also means the moon is further away from the sun or slightly closer to it. The moon rotates round the earth in the same way in an elliptical orbit. So sometimes it is closer to, and sometimes further away. If you add the two positions up further to the sun and further away from the earth you get an annular eclipse.

I can’t explain it more clearly. It is most difficult to think your way through how it works but I hope this makes sense.