What causes the crescent moon? See below?

Question

There has been so many questions along these lines in the last couple days that I thought I'd just have to pass on this picture.

See http://www.spaceweather.com/

It's a brilliant site anyway, with facts about impending solar flares (which sometimes result in Aurora). But look at the picture on the home page. It shows the crescent moon and you can just see the rest of the moon.

This is caused by Earthshine, and is reflected light from the earth lighting up the part of the moon that the sunlight cannot reach.

What you have to realise is that just after new moon, when the moon is a thin crescent, the sun is way, way behind the moon (it is 400 times further away), so most of its light is illuminating the backside of the moon, with just a little of it reaching the frontside making that brilliant crescent.

Answer 1

Hi. I agree. That site has a free sign up for email about upcoming events in the sky. I've gotten it for years. Did you realize that Earthshine is mostly reflection from the oceans?