Looking at the starry sky, you can see that stars differ in their brightness, or as they say astronomers, in its apparent brightness.

Most bright stars have agreed to call the stars 1-th magnitude; those of stars, which by its brilliance 2.5 times (or more precisely, in 2,512 times) weaker stars 1st values, received the name the stars 2nd magnitude. To the stars 3-th magnitude took those. who weaker stars 2nd magnitude 2.5 times, and so on, The weakest of stars visible to the naked eye, were numbered among the stars 6th magnitude. We must remember that the name "magnitude" refers not to the sizes of the stars, but only on their visible sheen.

You can count how many times the stars 1-th magnitude brighter stars 6th magnitude. For this you need a 2.5 to take a multiplier of 5 times. The result is that the stars 1st magnitude brighter on Shine of the stars 6-th magnitude 100 times. Only in heaven there is the 20 most bright stars, which usually say that the stars of the first magnitude. But this does not mean that they have the same brightness. In fact some of them are slightly brighter than 1 second value, others somewhat weaker and only one of them is the star in the accuracy of 1-St values

The same situation with the stars 2nd, 3rd and subsequent values. Therefore, to accurately indicate brightness of one or the other stars have to resort to the fractions. So, for example, those stars, which by their brightness are in the middle between the stars 1-St and 2-nd of magnitudes, is considered to belong to 1,5 stellar magnitude. There is a star with a magnitude of 1,6; 2,3; 3,4; 5,5 etc. In the sky you can see a few very bright stars, which by its brilliance exceed the brilliance of the stars 1-th magnitude. For these stars have introduced zero and negative magnitude. For example, the brightest star in the Northern hemisphere of the sky - VEGA - has the Shine of 0.1 magnitude, as the brightest star of all sky - Sirius - Shine minus 1,3 magnitude

For all stars visible to the naked eye, and many more weak accurately measured their magnitude.

Take ordinary binoculars and look into it to some area of the night sky. You will see many weakly glowing stars, not visible to the naked eye, because the lens (glass, light gathering in binoculars or telescope) more than the pupil in the human eye, and it gets more light.

In a regular theater binoculars easily visible stars to 7-th magnitude and prismatic field binoculars - stars to 9-th magnitude. In telescopes also seen many more slabovidyaschih stars. For example, in a relatively small telescope with a diameter of 80 mm lens) stars are visible to 12-th magnitude. In more modern powerful telescopes can observe the stars to 18-th magnitude. Photos taken using the largest telescopes, we can see the stars until 23-th magnitude. They 6 million times weaker on Shine the most slabovidyaschih stars that we can see with the naked eye. And if the sky with the naked eye available only around 6,000 of the stars, the most powerful telescopes can observe the billions of stars.