UNIT 1.- The Earth in the Universe
 
 The Solar System
 
    The Sun
     Mercury
     Venus
     Earth
     Mars
     Jupiter
     Saturn
     Uranus
     Neptune
     Pluto
     Ceres
     Moon
     Asteroids
     Comets
Asteroids and Meteors
Just past Mars there are millions of chunks of rocks orbiting the sun. They are not really rocks but are called asteroids. Asteroids are made of rocky material with some metals in it. This large group of asteroids orbiting the sun is called the asteroid belt. The asteroid belt is an area between the orbits of Mars and Jupiter. Most of the asteroids in our solar system are found there. They orbit the sun just as the planets do, but asteroids are too small to be planets. Astronomers think that the asteroid belt is made up of material that was never able to form into a planet. Some think that it's the remains of a planet which broke apart a very long time ago. The asteroid belt contains millions of asteroids. The largest asteroid is about one-fourth the size of our moon.
 

A meteor appears when a chunk of metallic or stony matter called a meteoroid enters the Earth's atmosphere from outer space. Air friction heats the meteoroid so that it glows. It creates a shining trail of gases and melted meteoroid particles. Most meteoroids burn up before reaching the Earth. Some leave a trail that lasts several seconds. Millions of meteors occur in the Earth's atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble.
     
 Images
   

A meteorite

The biggest meteorite ever found
Meteor Crater 3D