Every star is a ball of glowing gases which emits energy in the form of heat and light.Astronomers say that our Sun is a medium-sized star.Some stars are much larger and some are smaller than our Sun.
When we look at the night sky, we see stars of different kind. Some are bright while others are dim, some appears large while some smaller. Stars are known to be massive balls of fire. The appearance, brightness, size and other features depend mainly on temperature of the stars.
Stars get formed from collapsing clouds, gathering dust and gas. A star matures from the beginning of the collapse to adulthood. Most of the stars that we see today including the sun are termed as main sequence stars by the astronomers. Main sequence stars undergo fusion of hydrogen into helium in their core. Large stars have higher core temperatures than smaller ones. Hence they burn hydrogen very quickly compared to the small ones. Thus, life span of stars depends on its mass. Sun which is a massive star is in the main sequence and is said to burn for approximately 10 billion years. The Sun is about 4.5 billion years old now. It has another 5 billion years to burn the hydrogen fuel.
Not every star emits white light. The color of light that the star gives off again depends on its temperature. Some stars are red, some yellow, some white and some are blue. We know that the hot objects emit a continuous spectrum of light. For instance when a hot plate is slightly hot, it appears dull red and when too hot appears blue. Stars too emit light with different wavelengths (colors) which pass through the atmosphere. Hot stars emit red light while still hot ones emit yellow and the hottest emit blue or white. The brightness of the stars depends on how far it is from earth and how much energy it gives out.