An imprecise but systematic determination of the magnitude of objects was introduced by which Greek astronomer, geographer, and mathematician?
Magnitude (astronomy):  An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus. Hipparchus: Hipparchus of Nicaea ( ; Greek: Ἵππαρχος, "Hipparkhos" ;  ) was a Greek astronomer, geographer, and mathematician.
Hipparchus