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The Egyptians subdivided daytime and nighttime into twelve hours each since at least 2000 BC, hence the seasonal variation of their hours. The Hellenistic astronomers Hipparchus (c. 150 BC) and Ptolemy (c. AD 150) subdivided the day sexagesimally and also used a mean hour (1 24 day), simple fractions of an hour (1 4, 2 3, etc.) and time-degrees (1 360 day or four modern minutes), but not modern minutes or seconds.