What Makes the Stars Shine?

A star is a ball of very hot gas which shines by its own light. planets, as you know, and our moon, too, shine only by light reflected from the sun. And planets shine with a steady light while stars appear to twinkle. this is caused by substances in the air between the star and the earth.

the unsteady air bends the light from the star, and then it seems to twinkle. why does our sun shine? because it is star! And not a very big or bright star at that. Compared to all the other stars in the sky, it might be considered medium-sized and medium bright.

there are millions of stars that are smaller than our sun and many stars are several hundred times larger than the sun. they look small only because they are so far away. Ever since the days of the Greek astronomers, some 2,000 years ago, the stars have been divided into classes according to their "magnitude" or brightness.

Another way of grouping stars is a according to their spectra, or the kind of light that comes from the stars. By Studying the differences in these spectra, the astronomers may learn about the colors, the temperature, and even the chemical composition of the stars.  

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