Most of the people in this world know the term 'asteroid' and have a basic idea as to what it is. However, the real meaning of the celestial body is hardly known to anyone. Talking about asteroids, they are basically rocky and metallic objects in the Solar System that orbit the sun. Their size is such that they are considered too small for being planets and too large to be classified as meteoroids (which are usually defined as being not more than 10 meters across), unless they can be put into the category of comets.
There is one visual feature that differentiates asteroids from comets. The latter leaves a detectable coma, or tail, behind them, which the former does not. Asteroids are also known as minor planets or planetoids and can vary greatly in size, from a few hundreds of kilometers in diameter to just tens of meters across. Of the very large asteroids, some are almost of a spherical shape and look very much like planets, though miniature in comparison. However, majority of them are quite small in size and have an irregular shape.
As far as the physical composition of asteroids is concerned, a wide variety has been noticed. In fact, it has been difficult for astronomers to comment on the exact composition of asteroids. Still, some of them are solid rocky bodies, with a greater or lesser metallic content. Then, there are others that are nothing more than piles of rubble, which have been held together loosely by gravity. Asteroids are not visible to the naked eye, with the exception of one i.e. Vesta. It can be seen by naked eye, but only in very dark sky and when it is favorably positioned.
Of all the asteroids in the Solar System, majority can be found within the main asteroid belt, which lies between the orbits of Mars and Jupiter. At the same time, they have relatively low-eccentricity orbits i.e. their orbits are not very elongated. It has been estimated that the asteroid belt contain more than 750,000 asteroids that are larger than 1 kilometer across, apart from millions of smaller ones. All these asteroids are believed to be remnants of the protoplanetary disk. Some of them also have moons or are found in co-orbiting pairs, called binary systems.