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What is it?
There are many millions of stars in the sky. In the whole heavens, fewer than 6000 stars are bright enough to be visible and at any one time, less than 2500 stars are visible above the horizon.
Stars account for 98% of the matter in a galaxy. The rest of 2% consists of interstellar or galactic gas & dust in a very attenuated form. The normal density of interstellar gas throughout the galaxy is about one tenth of a hydrogen atome per cm³ volume. Stars tend to form groups.
What I shall discuss here?
There are many types of stars in the universe having different name & definitions. I’ll discuss a few of them!
Major kinds of Stars according to numbers
• Lone Stars :These are alone and going on their own. Lone stars are exception in the Universe.
These donot follow up the condition to be in galaxy. And this is the difference between it & Single stars.
•Single Stars These are found in galaxy & are single (for example Our Sun). These do not number more than 25% of Stellar (Star) Population.
•Binary Stars or Double Stars These exist as couples of stars (e.g., Antares in Scorpio is actually two stars) and they are some 33% of stellar population.
The rest are •Multiple Stars (e.g., Capella & Alpha Centuri comprize 3 stars each, while Castor consists of 6 stars).
Note that, stars which appear single to the naked eyes are sometimes double stars. There are two stars revolving around a common center of gravity. They are also found in orbital motion round each other, in periods varying from about one year to many thousands of years.
Vivid types of Stars according to their nature
When the hydrogen, the main element in a star, is depleted, its outer regions swell and redden. This is the first sign of age. Such stars are called Red Giants.
Our Star, the Sun, is expected to turn into a red giant in another 5 billion years. Red giants are dying stars that has expanded greatly from its original size and gives off red light. They have gigantic dimensions.
It is the blackened corpse of a star. Ultimately it disappears into the blackness of the space.
It is a tiny, dense, hot star, representing a late stage in the life of a star. The matter in it is so incredibly dense that a single teaspoonful of it would weigh several tonnes.
These are huge stars, with all their hydrogen fuel used up in their core, but continue to expand hundred of times bigger than its original size before they finally die.
Novae & SuperNovae
These are kind of stars, whose brightness increases suddenly by 10 to 20 times are more and then fades gradually into normal brightness. The sudden increase in brightness is attributed to a partial or outright explosion. In Nova, it seems that only the outer shell explodes, whereas in SuperNova the entire star explodes.
There are stars that show varying degrees of luminosity.
These are variable stars and are powerful quasi stellar sources of radio radiations.
These are also variable stars which emit regular pulses of electro-magnetic waves of very short duration.
© Gaurav Happy Tiwari, 2011