<P> The magnitude system dates back roughly 2000 years to the Greek astronomer Hipparchus ( or the Alexandrian astronomer Ptolemy -- references vary ) who classified stars by their apparent brightness , which they saw as size ( magnitude means `` bigness , size '' ) . To the unaided eye , a more prominent star such as Sirius or Arcturus appears larger than a less prominent star such as Mizar , which in turn appears larger than a truly faint star such as Alcor . In 1736 , the mathematician John Keill described the ancient naked - eye magnitude system in this way : </P>
who was the first man to classify stars according to their brightness
the Greek astronomer Hipparchus or the Alexandrian astronomer Ptolemy