Other Question #2875

Gary, a 45 year old male from Birmingham asks on August 7, 2005,

Why is the time of a day measured using 24 hours?

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The answer

Russ Rowlett, University of North Carolina at Chapel Hill answered on August 7, 2005

This question is answered in my Dictionary of Units on the H page under Hours. To put it briefly, the custom of dividing the daylight into 12 hours goes back at least as far as the Babylonians, who liked to divide units by 12 because groups of 12 are easily divided into halves, thirds, or fourths. Originally an hour was 1/12 of the time between sunrise and sunset, so summer hours were longer than winter hours. Later, when people wanted to express times at night, it was natural to divide the night into 12 hours as well, making 24 hours in the day. Only after the invention of mechanical clocks, around 1300, did hours became equal intervals marked by clocks.

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