A star is a huge ball of bright, hot gases. Stars contain a great deal of hydrogen which is their main source of energy. They also contain many different chemical element such as helium, nitrogen, oxygen, iron, nickel and zinc.
Stars come into existence in the vast clouds of dust and gas that move through the space. They begin to form when a large number of gas particles whirl together within such a cloud, These particles attract more particles and as the group gradually gets larger and larger, its gravitational pull gets stronger and they form a giant ball of gas.
As this ball grows, particles inside press down on those below them and pressure builds up inside the ball. Eventually the pressure becomes strong enough to raise the temperature of the gases and they begin to glow. When the pressure and temperature inside the ball become very high, nuclear reactions take place and these gases become a star. This process will take a few million years!
Our sun is a actually a star and it is about 109 times the diameter of Earth.
