The initial magnitude scale was established by Greek astronomer Hipparchus around 135 B.C.E., categorizing approximately 850 stars into six ranges from 1st (brightest) to 6th (faintest) magnitude.
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 ...