The first star catalog was made by the Greek astronomer, Hipparchos, in 150 BC.  He also created a system used to measure the  brightness of each star.  He gave each star a magnitude number.  The brightest stars were magnitude 1.  If they were slightly fainter, they were magnitude 2 and so on, down to magnitude 6.  

     Once the telescope was invented, we could see objects fainter than magnitude 6.  The scale had to be changed, so higher numbers were added.  For extremely bright objects, negative magnitudes were added.  

     Every 5 magnitudes represent a change in magnitude or brightness of 100 times.  For example, a magnitude 3 star is 100 times brighter then a magnitude 8 star.

Magnitude Scale    

-25   -20   -15   -10   -5   0   5   10   15   20   25

 The Sun -26.7

Full Moon -13.6

Venus -4.4

Sirius -1.4

Vega 0.03

Polaris 2.1

Naked eye limit 6

4" telescope limit 12

Space telescope limit 28