We live on the planet Earth. The earth is part of the solar(太阳的)system. The solar system is like the earth's neighborhood. The word "solar" means "related to the sun". The sun is at the center of the solar system. People used to think the sun moved around the earth. You can understand why. If you look into the sky, it sure looks like the sun moves!
But some early astronomers(天文学家)were against this idea. Nicolaus Copernicus was an astronomer in the 1500s. He was the first person to say that people were wrong. He believed the earth moved around the sun. In the 1600s, another astronomer named Galle o Galilei agreed. He built telescopes(望远镜) and observed the sky. He was sure that the earth moved around the sun. This caused quite a stir(骚乱)!Galileo was arrested(逮捕) .
It turns out that these early astronomers were right! The earth moves around the sun.
So do seven other major planets. These are Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. That makes eight major planets.
