The planets all travel around the sun. This is called orbit. They orbit around the sun. It takes the Earth one year to orbit the sun, or travel all the way around it. When the earth is traveling around the sun, the seasons change.

Mercury is the closest planet to the sun. The earth is the third planet from the sun. Pluto is the farthest planet from the sun. 

All of the planets and the sun together make up a big system called the solar system.

Planets are either made of rock or gas. There are nine planets in all.

A lot of people think that the sun moves, and this is what causes day and night. That isn't true. The earth turns, while it travels around the sun. This is what causes day and night. It takes 24 hours for the Earth to turn completely around. That's why we have 24 hours in a day. The side facing the sun has daylight, while the side away from the sun has night.

Think about it:  How many times in one year does the Earth orbit around the Sun? Does this number ever change?

To play a game about orbit, visit this site:  http://www.bigideafun.com/penguins/arcade/spaced_penguin/info.htm