When you look up in the sky and try to find out the brightest star? The number of stars you see is countless. But most of us can see about 6,000 stars without a telescope, and one-quarter of them are too far south that can be seen in North America. 2,000 years ago, ever since the days of the Greek astronomers, the stars have been divided into classes according to their magnitude or brightness. With the invention of the telescope, only six magnitudes, or degrees of brightness, were recognized. A star of the first magnitude is the brightest, and stars of the sixth magnitude the faintest. Stars fainter than the sixth magnitude cannot be seen without a telescope. There are 22 stars of the first magnitude, and the brightest star of all is Sirius, which has a magnitude of -1.6. This makes Sirius over 1,000 times brighter than the faintest star that can be seen with the naked eye. The lower we go down in magnitude; the more stars there are in that class. Thus, there are 22 stars of the 1st magnitude and about 1,000,000,000 stars of the 20th magnitude.