The main source of energy for the stars is the thermonuclear fusion of hydrogen in its core. The core which mainly consists of hydrogen, helium and traces of heavier elements gets compressed under its own gravity until it reaches a particular temperature and sufficient internal pressure builts up to trigger the nuclear reaction. Once the reaction starts, the star is all set to shine and radiate heat for the next few million years. The star’s internal pressure prevents it from collapsing under its own gravity. Once all the hydrogen in its core gets exhausted, another set of nuclear reaction starts in which helium fuses to form heavier elements.
Stargazing Again : Observe a few bright stars closely with the naked eye for a little while. You can easily determine their color. Yes!!! Stars vary in their color too…Depending on the temperature, the color of stars may be blue, white, yellow, orange or red. The hottest stars are blue and the coolest ones are red. According to the surface temperature, stars are classified into 7 classes :
Class O, B, A, F, G, K, M. Class O stars are the hottest and Class M stars are the coolest. The Sun is a yellow, Class G star.
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