Millions of small rocky bodies called asteroids are present in the solar system. If the asteroids were "luminous", we shall see as all stars in the night sky.
A significant portion of them circulate in a ring between the orbits of Mars and Jupiter, between 2 and 4 AU (symbol: AU) The distance averages of the Earth in the Sun. An AU is worth 149 597 871 km. It is a unity often used for the distances in the solar system, or for the space of two stars in a double system. , called the asteroid belt. It marks the boundary between the terrestrial planets and gas giants.
An asteroid is a celestial object is not observable to the naked eye, because of its small size which varies from a few tens of meters to several hundred kilometers in diameter and is part of our solar system.
Objects of less than 50 m in diameter are called meteorites. Asteroids are not satellites of planets.
These debris of the protoplanetary disk, not being sufficiently numerous and massive, failed to consolidate sufficiently to form a planet, during their building. Asteroids are of great importance in understanding the formation of the solar system, it is for this reason that astronomers show a strong interest in the study of these objects.