The moon doesn’t look as if it’s very far away, but its distance from the earth averages 239,000 miles. The diameter of the moon is 2,160 miles, or less than the distance across the United States. But when the moon is observed with a very large telescope, it looks as if it were only about 200 miles away.
Because the moon seems so close and big to us, we sometimes forget that 239,000 miles is quite a distance away. It is this great distance that explains why the moon seems to follow us when we drive in a vehicle and look up at it.
To begin with, our feeling that this is happening is just that-only a feeling, a psychological reaction. When we speed along a road, we notice that everything moves past us. Trees, houses, fences, the road all fly past us in the opposite direction.
Now there’s the moon, part of what we see as we look out, and we naturally expect it also to be flying past us, or at least to be moving backward as we speed ahead. When this doesn’t happen, we have the sensation that it is “following” us.
But why doesn’t it happen? Because the distance of the moon from the earth is quite great. Compared to the distance our vehicle travels in a few minutes, that distance is enormous. So as we move along, the angle at which we see the moon hardly changes.
In fact, we could go along a straight path for miles and the angle at which we would see the moon would still be basically the same. And as we notice everything else flying past, we get that feeling of the moon “following” us.