Astronomy:Cycles and Seasons
Life on earth works through cycles and seasons. Once a day the earth rotates around its axis. Once a month the moon orbits the earth. And once a year the earth revolves around the sun. We call the ends of the axis around which the earth rotates the north and south poles. The earth also rotates on an angle. Seasons are caused by the earth's tilt and movement. And tides are caused by water responding to the gravitational pull of the sun and moon.
- Added：2006
- Country：Australia
- Duration：20
- Time of update：2011/3/11 15:03:55