e twelve divisions of the day, came to Hellas not from Egypt but from Babylonia." Then, during the fifth century B.C, Meton observed that the sun-dial's gnomon inaccurately measured the sun's course; thus, at least for the purposes of astronomy, the solar day was inadequate. In addition, it was noted that the solstices and equinoxes do not divide the year up into four parts. Because of astronomer's need to make exact calculations, an average day of "mean" length was created. This time period contains an artificial meridian at midday and is divided up into equal parts--otherwise known as "equinoctial" hours--based on day length at the equinox: both night and day together eventually were divided into 24 equal parts throughout the year. With time, even the hour was subdivided: its sixty equal parts were each again divided by sixty, thus giving rise to minutes and seconds.
Mean or equal hours do not correspond to the sun-dial's solar hours. For example, on February 11, mean time is ahead of the sun-dial by over 14 minutes. Conversely, on November 3, mean time lags behind solar time by approximately 16 minutes. Solar and mean time coincide on the following days: April 15, June 14, September 1, and December 25. These developments eventually led to "Greenwich time".
Meanwhile, the Chinese developed their own system of time. It is not known whether or not the Chinese system derived from some form of Babylonian time. Although as with other civilizations, the Chinese system subdivides the day into equal parts, the oriental day begins at sunset. Like the Babylonians, the Chinese day could have also been suggested by the division of the year into twelve moons. Eventually, the system spread to Japan, where it remained in force until the recent introduction of European time.
These early subdivisions of time evolved as a result of human need. Astronomers and astrologers analyzed time so that they could predict the pos...