When we look up at the sky, we do not see too 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 senes.
The blue stars are large and hot and bnlliant. Their surface tem- peratures 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 as 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 cannot be seen without a telescope. Stars of the first magnitude are the brightest, and there are about 20 such stars we know of. But their arc at least a thousand million stars that are only of the twentieth magnitude.
What Is The Brightest Star?