Stars are massive heavenly bodies which are made of plasma and held together by gravity. They are present in billions in our galaxy and vary in their types. Some exist in pair or even triplets while others are standalone. Many of the stars have heavenly bodies rotating around them, forming a system similar to our solar system. Stars are classified on the basis of their size, color and intensity and temperature. However, these factors are dependent on the amount of matter available at the birth of a star and its age (Bennett, Donahue, Schneider & Voit, 2000).

A star passes through various stages in its life during which it changes its size, color, intensity and temperature. All stars are born in nebula. Over the time, the hydrogen gas present in the nebula is pulled together by gravity and begins to spin. As the spin accelerates, the gas begins to heat up and takes the form of a Protostar. Eventually the temperature reaches so high that it triggers nuclear fusion reaction in the core of the Protostar causing it to glow. As the time passes, its brightness increases and it contracts in shape but then becomes stable (NASA, 2004).

Once the star stabilizes, it is said to be in the main sequence. In the main sequence all stars show stability in the rate at which they convert hydrogen into helium. However, it continues to contract slowly over billions of years to compensate for energy and heat it has lost. This contraction continues to increase the temperature, density and pressure at the core of the star which balances the pull of gravity and stops the star from collapsing. This tussle between the gravity pulling and gas pressure pushing out continues for the whole life span of the star (The Aspire Lab, 2009).

The continuous conversion of hydrogen to helium results in its depletion. Once the whole supply of hydrogen runs out, the nuclear fusion reaction at the core of the star stops and the core begins to contract due to loss of pressure. The outer layer of the star, which is also mostly hydrogen, begins to expand and cools down emitting red radiations. The star is now said to be a Red Giant. This red giant continuous to expand out for some time and its outer layer is expelled into the space as nebula (Bennett, Donahue, Schneider & Voit, 2000)………………………………………………..
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