Main Question or Discussion Point
Why do planets rotate around the sun? due to the gravitational field of the sun, which is obvious, but why do they not gradually crash into the sun, due to their motion and the loss of energy after a while ?
The loss of kinetic energy in the rotation of the Earth is due to the combined Earth-Moon system. The Earth and Moon will eventually become tidally locked with each other (the Moon already presents a virtually identical face towards the Earth). The Earth's rotation rate gradually slows down and the distance between the Earth and Moon gradually increases (the combined angular momentum has to stay constant). The varying rotation rate is why leap seconds are required.rbj said:check out what "leap seconds" are all about. the need for an occasional leap second, here or there, is due exactly to loss of kinetic energy in the rotation of the earth.
there is kinda an odd reason (having to due with geology and the speed of the Earth's crust) for why they haven't added leap seconds in the past few years. but the rotation of the earth, as a whole, is still slowing down very minutely.
that is absolutely most correct. i only tried to imply that there the matter in space that slows down the rotation will also slow down the revolution about the sun. i don't think any human beings will be left (it will take a while) if it slows to the point of crashing into the sun.pervect said:Slowing down the rotation of Earth isn't going to cause it to crash into the sun, though.
sorry for being non-careful.A careful answer would involve figuring out all the effects that might brake the Earth's orbital motion (there are some), plus the effects that would move the Earth into a higher orbit (there are some of those, too).
A non-careful answer would say that these effects are all so small that we can expect the Sun to turn into a red giant first, at which point the question becomes moot.
no. it's clear that they are measuring a net loss of angular momentum.BobG said:The loss of kinetic energy in the rotation of the Earth is due to the combined Earth-Moon system. The Earth and Moon will eventually become tidally locked with each other (the Moon already presents a virtually identical face towards the Earth). The Earth's rotation rate gradually slows down and the distance between the Earth and Moon gradually increases (the combined angular momentum has to stay constant).
yes. and the variation is generally a negative trend.The varying rotation rate is why leap seconds are required.
they've never been subtracted. only added. there haven't been any added since the 90s because of some geological phenomenon that is, for the time being, causing the rotation of the earth's crust to have accelerated slightly.The reason they haven't added leap seconds is buried deep in the article (it's not very well organized, even though it pulled together some good material). Primarily, it's because it's becoming more important for systems that have to communicate with each other to be using the same time and, unfortunately, leap seconds have to be added in (or subtracted) manually at irregular times.
they have to decide what the designated days are and i don't think they have any days slated for a leap second yet. they don't want to subtract any (because of the recent crust acceleration) if they have to add them back later (because of the general deceleration).You'd think it wouldn't be that difficult to add in the leap second at 0000 Universal Time on the designated day, but ........... if a computer can't do it automatically, then it must not be a very good thing.