A planet is a world that travels around, or orbits, a star. The Sun is a star, and planet Earth travels around it. There are 9 planets, about 60 moons, dust and thousands of lumps of rock, called asteroids, traveling around the Sun. All these objects together are known as the Solar system.
Besides traveling around the Sun, each planet rotates on its own axis; this means it goes round and round itself all the time in space, creating day and night. Earth rotates around its axis once every 23.93 hours. It travels around the sun every 365.25 days. Planet Pluto, however, needs 247.7 Earth years to travel around the Sun.
The Universe is unimaginably huge. Scientists believe it began 14 billion years ago, but our Solar system is only about 4.3 billion years old. Our Solar System formed from a cloud of gas and dust. The cloud was pulled together by gravity and a shock wave from a neighboring Super Nova. Most of the cloud turned into what is now the Sun, and the rest made the planets, moons and asteroids.
Our Solar System is but a tiny part of a galaxy (a group of stars) called the Milky Way. There are more than 200 billion stars in the Milky Way and our Sun is just one of them. The Milky Way Galaxy is just one of more than 10 billion galaxies in the Universe.
© 2005 Al Bawaba (www.albawaba.com)
