Question: Why doesn't the earth spin in the opposite direction?

Sara Imari Walker answered on 15 Jun 2011:

Hey cai! You are full of great questions!! Most bodies in the solar system spin the same direction as the Earth. The reason has to do with how the solar system formed. The solar system formed from a massive clump of gas and dust. This cloud was spinning initially (maybe a star glanced by it and set it in motion) and as gravity acted to compress it it started to spin faster. This is the same thing as how ice skaters spin faster with their arms in than when they have them out-stretched, the principle is called conservation of angular momentum. So planets, the Sun, and Earth all got their spin from conserving angular momentum as this giant cloud collapsed to form our beautiful solar system. So most planets spin in the same direction. There are a few notable exceptions though. One is Venus which spins in the opposite direction. The other is Uranus which is actually on its side relative to all the other planets. All planets and the Sun have their spin axis aligned (point up say) and Uranus’s points to the side! Probably both Uranus and Venus got their unusual spins from impacts with other objects in the early Solar System before things settled out.