A:

It's called angular momentum and like ordinary momentum, with a bit of twist, is a conserved quantity. That's why ice skaters, when starting a spin with their arms outstretched, spin even faster as they draw their arms inwards. A related question is "Where and when did the sun acquire its intrinsic angular momentum?". Now that's a complicated question being debated even today about the origins and development of the solar system. There are a number of theories with different details but the gist is that the dust cloud that was the beginning of the solar system had a bit of excess angular momentum. As the sun and the planets formed this total angular momentum was shared amongst the planets and the sun. Curiously enough, the orbital angular momentum of the planet Jupiter has most of the total in the solar system, the sun has only a few percent.LeeH

(published on 07/24/2008)