News about the moon

The things you learn in the 57th grade.

Last week I learned that the moon rotates. Well, it doesn’t actually rotate, but it appears to.

We can see the moon from our bedroom window when it rises late in the southeast sky, which it was doing last week. I was watching it about 2 a.m., a white crescent pointed down at the dark horizon. The crescent was “on its back” enough to form a cup that would hold water. I am told it is good luck, seeing a crescent moon that will hold water.

It occurred to me that the moon was pointing me toward the sun. With a little geometry, I could draw a line through the crescent’s median, and that line would take me straight to the sun. (Hey, it’s better than worrying about taxes). Doing so, I reckoned that the sun was way on the other side of the earth, somewhere over Italy, maybe.

Of course the reality was that the sun was in its usual position, 93 million-odd miles away in space, and that was the location to which the moon was pointing. I visualized earth, moon and sun in their space relationships. I saw the sun as relatively stationary. I know it was moving through space in two or three directions, at unimaginable galactic velocities, but from my bedroom in San Diego County, I figured I could think of it as practically stationary for the next four hours.

But the earth was moving. We were rotating, west to east, at a speed that would spin us into position for dawn and sunrise around 6:15. Thinking this, I looked at the moon again. The crescent was pointed at a severe angle down toward the ground. If the crescent pointed toward the sun, then by 6:15, the crescent would be pointing not down, but east, not because the moon was rotating, but because we were.

At that point, my thinking locked up. It didn’t seem reasonable to me that the crescent moon could rotate, in such a way that I could actually watch it happening. It seemed to give me too much power, too much knowledge of the intimacy of the sun-moon relationship. For a minute, I thought about staying awake, to watch and verify.

But I didn’t. At 5:30, we woke up, fed puppies and kitties, made coffee, and then went outside for glider time. It was a few minutes after 6, still easily dark enough to see the crescent moon. Naturally its position had shifted higher and toward the west. But the crescent had also rotated. The cup would not hold water. It was pointing not down, but toward the eastern horizon, where the sun was set to appear. Between 2 and 6, the moon had spun in the sky. In all my time on the planet, all those nights and mornings watching the moon, the idea of such a phenomenon had never crossed my mind, and I wondered: how many other people know about this?