Asteroids are bodies of matter that orbit the sun, just as the planets do, but they are too small to be actually called planets. Scientists have many theories about the origin of these celestial bodies. One of these theories is that they are left over material from the formation of the planets, while another suggests tat asteroids are the remains of a planet that disintegrated for some reason.
In astronomy, asteroids are referred to as minor planets. Some of them have been named, such as Ceres, which is over 1000 km in diameter. There are asteroids that are only about the size of a pebble, but most of them measure about 240 km. While there have been discoveries of asteroids from the orbit of the Earth to Saturn, the majority of them are within a belt between mars and Jupiter.
There have been times when asteroids have collided with Earth. Then they are called meteorites, producing meteors that streak through the night sky before disintegrating. Usually these meteorites burn up before they come within 30 miles of the Earth’s surface, but some of the larger ones have crashed to earth, causing a crater or basin. Meteorites that have landed on Earth have been closely studied and examined. They are usually composed mostly of rock containing mineral, such as silicon and iron.
There are numerous asteroids in space. About 1700 of them have been named, even though it is possible to see hundreds of thousands of them through a telescope. Astronomers do not usually name an asteroid until they can determine its orbit. Asteroids do rotate on their own axis and for those that have been named, this ranges from 3 to 10 hours. There is a difference in the length of time it takes them to revolve around the sun, as well, which could be anywhere from 643 days to 5000 days.
The brightest of the asteroids is Ceres, which was also the first one to be discovered in 1801. Ceres, Pallas, Juno and Vesta make up the Big Four because of their size and brightness. It is possible to see Ceres with the naked eye.
Through space exploration and the use of space probes and satellites, scientists have been able to take images of asteroids. Vesta, for example, was closely studied by means of the Hubble Space Telescope.