OUR GALAXY-THE MILKY WAY

WHAT ARE STARS?

Since the earliest time, people have been watching the night-sky. They saw the moon and stars moving across the sky and wondered. They were always curious to know what they are and why they move. So, they gave them names and made up interesting stories about them too. Most of these names are Greek, Indian and Arabic.

WHAT IS A STAR?

A star is a shining ball of gas. It is formed when a cloud of hot gas and dust condenses into a globe-like form. The heat of a star comes from its deep inside where hydrogen has turned into helium. This helium gives out nuclear energy.

Most stars shine regularly for thousands of years before they run short of fuel and extinguish. Stars can be classified into three chief groups-very hot stars, medium stars and cooler stars.

The hot stars shine emitting a bluish light while the cooler stars look reddish. Medium stars look yellow in color. We can see these colors in many stars that can be seen with the naked eye.

The color of a star tells a lot about it. Sometimes a star may start giving off more light and grow into a red, yellow or even blue giant star. Not only this, it may grow even larger and hotter to become a super-giant star. A star that Ioses its energy and shrinks in size, shines only dimly. Such a star is called a white-dwarf. Further shrinking and cooling may make it a black dwarf.

In all, there are at least 100,000 million stars in our star system. But with the naked eye, one can see about 3000 stars at one time.

A star, if it explodes, is called a supernova. It may condense into a black hole or a neutron star (pulsar). The former has a thick core while the latter has a thinner one. Two stars that are nearest our earth are the Sun and the Proxima Centauri.