The first observer to catalog differences in star brightnesses was Greek astronomer Hipparchus. He created a catalog around 135 b.c. of roughly 850 stars divided into six ranges. He called the brightest 1st magnitude and the faintest 6th magnitude. Observers noted that 1st-magnitude stars varied greatly in brightness. Also, to assign a magnitude to the brightest planets, the Moon, and especially the Sun, scientists would have to work with negative numbers.