> > The earth rotates on it's axis once in 24 hours with respect to the sun. But with respect to the background stars, it is a little less. This is called a siderial day. Trusting my memory on that, I think it is about three minutes shorter than a solar day.
>
> The Earth's rotation is about 23 hours, 56 minutes, 4.091 seconds if I remember rightly. Is that spelt siderial or sidereal? I can never remember.

Hang on a second. I was with this thread until right now. Now I'm wondering if I'm wrong, or I'm just misunderstanding someone.

I thought that hours, minutes, and seconds were *defined* by the earth's rotation, such that the earth does, in fact, rotate 360 degrees in EXACTLY (or essentially) 24 hours. I thought the reason the stars appear in the same place in the sky four minutes earlier every night was because of the earth's *revolution* around the sun. Such that, after six months, the stars you saw at midnight are now hidden by the sun at noon.

Now we're saying the earth's actual rotation is four minutes shy of 24 hours?

My head is starting to spin. Somebody fix me.