Asteroids and comets

The Sun and the planets are nearly round, but the Solar System also has many small, rocky, irregular objects called asteroids. Many go around the Sun between the paths of Mars and Jupiter: this region is the asteroid belt. Sometimes an asteroid passes very close to the Earth.

Sometimes visitors come from the outer Solar System: comets, with long tails. Comets are made of dust, gases, rocks and ice. As a comet comes close to the Sun, its frozen material starts to evaporate, and this forms the tail. As it moves away from the Sun it grows dim, until we can no longer see it with our eyes alone. Many comets come back again and again. The famous Halley's Comet appears about every 76 years; it was last seen in 1986.

So the Solar System is the Sun, eight planets, their moons, and many smaller objects, including asteroids and comets. The Sun is the largest and heaviest object in it and produces almost all of its energy. Everything else shines only by reflecting the sunlight that falls on it.

Other stars are not members of our Solar System. Sirius, for example, is a star far beyond it.