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What is the baseline for determining the magnitude scale of celestial objects? Why do brighter objects have negative numbers?

Dean Treadway, Knoxville, Tennessee
RELATED TOPICS: STARS | OBSERVING
Astronomical-brightness
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.

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