Sigh.
If the Moon were stationary in the sky, but the Sun continued to rise and set on the Earth, would one claim that the Earth was not rotating?
What's interesting is that if the moon rotated in 28 days or 30 days, there would be no question that it rotated on it's own axis since we would, over time, see its entire surface. But since it's synchronous with it's orbital period around the earth at 29 days, people can't seem to grasp that it's turning on its own.
It's turning in the sense of "spinning or rotating" on an autonomous orbit around the Earth. It is not SPINNING on ITS OWN axis.
Quoting: mclarek 971744Yes, it most absolutely is. If you stood at the north pole of the moon and looked directly overhead at the sky, what would it appear to do over a 29 day span?
Also, would you say the moon was not rotating on its axis if it's rotation period was 10 days and we saw both "sides" of it every couple of weeks? Or if it were rotating every 40 days and again we saw all sides of it? Why is it that you think it doesn't rotate just becuase its period of rotation is 29 days?
And, you have the reason for libration wrong as well. The moon's orbit around the earth is an ellipse, not a circle. Since it travels at a roughly constant speed in its orbit, we get to peek around the sides a bit over its cycle since for parts of that ellipse, it's orbital speed is NOT completely synchronous and the moon SPINNING ON ITS OWN AXIS is a bit too fast or too slow and shows us a bit more of one side and then the other. If its orbit were perfectly circular, there would be no libration.
Also, your idea that the earth spins "on a spot" is not correct either. It rotates around the barycenter of the earth/moon system, which is NOT at the earth's center but off to one side towards where the moon is. So, if you were to look at teh earth's orbit around the sun from "overhead", it would appear to trace a sine wave along it's circular path. The sun exhibits this same action because of the mass of Jupiter. That's how we detect planets orbiting around distant stars...by tracing the proper motion of the star and doing a fourier transform on its motion to calculate how many and what mass planets are orbiting it.
You REALLY need to bone up on your Astronomy 101.
