Astronomy:Stallites, Orbits and Gravity
In the solar system, there are nine planets. They revolve around the sun along regular orbits. The earth is one of the nine planets, and it has a moon travelling around it. The other eight planets have moons travelling around them, too. Nowadays, people have sent hundreds of satellites into the space. These satellites also revolve along regular orbits. And we have a few astronauts working and living in the space station.
- Added：2006
- Country：Australia
- Duration：20
- Time of update：2011/3/11 15:03:55