A Star is a self luminous body emitting light and heat like the sun. some stars are larger and more brilliant than the sun but they are at a very large distance from us and appear to be very small. Temperature inside the stars at their centers is in million of degree centigrade. So in stars matter exists in gaseous, plasma state. These stars contain very large amount of hydrogen, helium and few other gases in small portion.
As the temperature is very high, hydrogen nuclei collide with each other and convert into helium. This process is called fusion reaction . Due to this nuclear fission reactions, light and heat are emitted. These stars also have life cycle. After some billions of years, some of the stars suddenly cease or stop emitting light. They are said to be dying stars.
We can see about 3000 stars with our naked eye. With the help of telescope we can see thousands of million of stars.
a number of stars can be grouped together with an imaginary out line to match some human or animal figure. These groups of stars are called constellations. at present 88 constellations have been recognized. some of these are Orion, Cygnus, Ursa major or great bear.