So the moon's orbit is nearly, but not quite circular?In other, related, news : there are no spherical objects in nature. Nor are any of the platonic solids perfectly realised on this material plane...
From the point of view of an observer standing on the Earth, the Sun orbits us. Also, if your measurement device is a thumb, then the measurement error will be large enough to cover quite a lot of ellipticity! :)
What I can never quite understand is that the moon is rotating (I think) but we always see one face - tidally locked? Is that right?
(From the point of view of an observer standing on the Earth, the Sun orbits us. Also, if your measurement device is a thumb, then the measurement error will be large enough to cover quite a lot of ellipticity! :)
What I can never quite understand is that the moon is rotating (I think) but we always see one face - tidally locked? Is that right?
The Alchemist king of the needlessly complicated,
Thu 15 Apr 2010, 13:26,
archived)
Yep, very, very nearly circularBut not exactly. Same with planetary orbits around the sun. I think Venus' is the nearest to circular. Mercury's is totally whacky; back in the day they thought there was an extra planet (they called it, err, Icarus I think) inside Mercury's orbit. Turns out that that was one of hte first great proofs of general relativity because it gets Mercury's orbit almost exactly right while Newtonian gravity is just wrong.
Though I think you're right that if your measuring tool is a thumb at arm length then the errors are likely to be a bit more significant than a negligible ellipticity :) I *was* being pointlessly pedantic.
I'm ashamed to say I've never actually understood tidal forces. I know what they *are* (I can even work it out relativistically), I know where they come from and all that, but I actually don't understand how they've locked the moon's rotation to us but apparently it's true. I may figure that out at some point.
(Though I think you're right that if your measuring tool is a thumb at arm length then the errors are likely to be a bit more significant than a negligible ellipticity :) I *was* being pointlessly pedantic.
I'm ashamed to say I've never actually understood tidal forces. I know what they *are* (I can even work it out relativistically), I know where they come from and all that, but I actually don't understand how they've locked the moon's rotation to us but apparently it's true. I may figure that out at some point.
boris the spider,
Thu 15 Apr 2010, 13:35,
archived)
Did you see that they've found some exoplanets that rotate in the opposite direction to their star?I didn't know that this wasn't meant to happen, but apparently it wasn't (although now they know it can).
( The Alchemist king of the needlessly complicated,
Thu 15 Apr 2010, 13:41,
archived)
actually no i didn't hear a thing about thatif i get what you mean you mean the star's rotating clockwise and the planet is orbiting anticlockwise? that's really hard to explain. it's like you start off with everything on a big roundabout that then splits up. all the individual pieces are still going to orbit in the direction that it was spinning in. or if you mean that the planet itself is rotating opposite to the star... i didn't know anyone had got enough of a handle on a planet's atmosphere to tell which way it was rotating! that'd be fantstic.
any ideas of a link or anything?
(any ideas of a link or anything?
boris the spider,
Thu 15 Apr 2010, 13:45,
archived)