The first observer to catalog differences in star brightnesses was Greek astronomer Hipparchus. He created a catalog around 135 B.C.E. of roughly 850 stars divided into six ranges. He called the ...
Cepheid stars have predictable brightness changes linked to their periods. This period-brightness relationship lets astronomers calculate a Cepheid's distance. Hubble found a Cepheid in the Andromeda ...
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