How is stars brightness measured from earth?

Astronomers use a special term to talk about the brightness of stars. The term is "magnitude". The magnitude scale was invented by the ancient Greeksaround 150 B.C. The Greeks put the stars they could see into six groups. They put the brightest stars into group 1, and called them magnitude 1 stars. Stars that they could barely see were put into group 6. So, in the magnitude scale, bright stars have lower numbers.