Riding the sky

Taking the trash out the other night, I did what I always do: I looked up. The crescent Moon was setting, and I could see the Summer Triangle easily (after a few minutes, when my eyes adjusted a bit, I could see the Milky Way piercing through, too). As I walked back in, I happened to turn to the east. I could see the big square that marks the constellation of Pegasus, and to its lower left, the two curved lines of stars denoting Andromeda. Instantly, I saw something wrong. Andromeda doesn't have two stars so close together, I thought. Ah, I realized a second later, one of them must be a satellite. Sure enough, as I watched, one of the stars could be seen to be moving. I had a moment of disorientation when it was hard to tell which star was moving away from the other, but after ...