Given that the Moon is locked with the Earth, is it true to say that the Moon rotates? I’m assuming the point of reference is the Sun. The Earth rotates when compared to the Sun, but does the Moon? It revolves around the Earth like a figure skater, exposing its surface to sunlight over the period of its revolution, but it’s not actually rotating in one place, is it?
Note: I love astronomy, lifelong fan, A student… yet this has always been one of those little things that I just never seem to grasp.
Cecil states that the moon is moving away from the Earth at a rate of 4 inches per month. At this rate, the moon would only be about 330 million years old! The actual rate the moon is pulling away from the Earth is closer to 4 centimeters per year. Still not very fast, but much slower than stated in the article.
Cecil states “the moon continues to recede from us … at the rate of just four inches per month” (48 inches per year). NASA claims “the Moon is receding from Earth at a rate of about 3.8 centimeters per year” (1.5 inches per year). Cecil needs to set NASA straight.
Yes, the moon rotates both with respect to the Earth and with respect to the Sun. A lunar day (the rotation with respect to the sun) lasts about 28 Earth days.
There’s an image on this page at HowStuffWorks.com that might help you out.
If you keep in mind that the same side of the moon is facing the Earth at all times, it should be clear that the moon must be rotating with respect to the Sun.
I would have thought that whether a thing rotates or not isn’t relative to any external objects–it’s just the question of whether its parts are accelerating in relation to each other in a certain way, isn’t it?
It actually seems there are two different subjects in this one thread.
Does the moon really rotate?
Cecil made a mistake in the article.
The answer to #1 is that, yes, the Moon rotates, even from the reference point of the Sun. The only reference point from which you might be able to say it doesn’t rotate is from the Earth. But that’s a rotational reference frame, as the moon is revolving around the Earth. While there is no absolute frame of reference, a rotational frame is usually not used. It would be like saying that the tires on your car don’t rotate because they don’t move relative to the wheel.
The response to #2 is that, yes, Cecil was off by a factor of 30. But, remember, all mistakes are Ed’s fault.
At some point in the editing process - undoubtedly a point in which I was involved - 4 centimeters per year morphed into 4 inches per month. It has now morphed back. My apologies to the Teeming Millions and to the Master, who assures me the welts will soon go down.
The moon goes around the Earth. As it does so, it maintains the same face toward Earth. Because on one day the side toward Earth is also toward the Sun, and 14 days later that side toward Earth faces away from the Sun, you can tell that the Moon is rotating.
Rotation does not require the object to sit still. It can be rotating and moving in a linear direction. Like a top - it spins fast enough to stand up, so clearly it is rotating, but it can also get slightly off balance and wander around. That movement does not negate that the top is rotating about its own axis, just means that the axis of rotation is moving. Same way the Earth rotates once a day, but is also orbiting the Sun, so it is constantly in motion. The Moon also is rotating about its own axis, and the axis of rotation is orbiting the Earth and the Sun.
“When you you think NASA will land on the sun?”
“They can’t land on the sun, it’s too hot-- the spaceship would melt!”
“Well, they just have to do it at night.”