Part of the show Sun Tans, Fission and Fusion
David in Tillingham asked:
Sitting in my kitchen which faces west, I can see the sun well up in the sky and I can also see the moon. But the moon still had a shadow on it. Where did the shadow come from if I can see the whole disk of the moon?
The reason for that is that the shadow you're seeing is the edge of the Earth and so because one isn't completely in line with the other, you don't see the whole disk. The moon is 240 000 km away and from your vantage point you can just peer round to the dark side. We're sat on the sunward side of the planet and if you look across at a planet that's more or less the same distance from you, you can just peek around the dark side of it.