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date: 23 January 2021


  • A. T. Grafton


Ancient culture knew a range of expedients for dividing the twenty-four hours of the day, for marking the succession of days in the month or year, and for dating important historical events. *Hesiod already used the rising of particular *constellations to mark the changing seasons, and ascribed propitious and unpropitious qualities to the days of the month that corresponded to the phases of the moon. By the 5th cent. bce, Athenian astronomers—like their Babylonian colleagues—knew that the lunar month is approximately 29½ and the tropical year approximately 365¼ days long, and could divide the day and night up into twelve ‘seasonal’ hours that varied with the length of daylight. Astronomers (see astronomy) from *Meton to *Hipparchus (3) and *Ptolemy (4) developed increasingly accurate luni-solar cycles and learned to explain and predict solar and lunar *eclipses. They also created parapēgmata, or public calendars, which traced the risings and settings of stars and predicted weather throughout the year.

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