Why are Some Stars Brghter than Others?

When we look up at the sky, we do not see to many differences among the stars. some look a bit bigger, some are brighter than others. but we really cannot get a good idea of the tremendous differences that exist among them. one way of classifying stars is by their spectra a spectrum is a breakdown of the light given off.

In this way, stars range from blue stars to red stars. our sun is considered to be yellow, and is in the middle of the series. The blue stars are largest and hot and brilliant. Their surface temperatures may be as high as 27,750 degrees or more. The sun is medium bright and has a surface temperature of about 6,000 degrees.
Red Stars are rather cool and have surface temperatures of  1,650 degrees or less. So you can see that some are very much brighter than others, but because of their great distance from the earth we are not aware of it.

The brightness of a star is called  its "magnitude". a star of any given magnitude is about two and a half times fainter than a star of the magnitude above it. So magnitude is a sort of scale for measuring brightness. Stars fainter than the sixth magnitude can not be seen without a telescope. Stars of the first magnitude are the brightest, and there are about 20 such stars we know of. But there are at least a thousand million stars that are only of the twentieth magnitude.

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