The factor of 60 comes from the Babylonians who used a sexagesimal (base-60) numeral system. However, the Babylonians did not subdivide their time units sexagesimally (except for the day). The hour had been defined by the ancient Egyptians as either 1/12 of daytime or 1/12 of nighttime, hence both varied with the seasons. Greek astronomers, for example Hipparchus and Ptolemy, defined the hour as 1/24 of a mean solar day. Sexagesimally subdividing this mean solar hour made the second 1/86,400 of a mean solar day. 