I was given this problem by my teacher: "It's about 1.496x10^8 km from the Sun to the Earth, and about 384 000 km from the Earth to the Moon. So when there is an eclipse of the moon, how far is the Moon from the Sun?" Before this he says this is a sneaky one, but it seems simple. If the moon is eclipsed, it's behind the earth, so all I need to do is add the length between the Moon and the Earth with the distance between the Earth and the Sun. Is there something I'm missing?