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Due to the continuous change of the duration of daylight over the course of the year, the duration of the day division, i.e. the temporal day hours and the temporal night hours, also changes over the year. The temporal hours of day and night are equal only at the spring and autumn equinoxes.
The 12-hour clock can be traced back as far as Mesopotamia and ancient Egypt. [7] Both an Egyptian sundial for daytime use [8] and an Egyptian water clock for night-time use were found in the tomb of Pharaoh Amenhotep I. [9] Dating to c. 1500 BC, these clocks divided their respective times of use into 12 hours each.
Dial of a wall-mounted sundial for simultaneous display of temporal (twelve hours, black) and equinoctial (red, digit at end of hour) daytime hours (At day-night equinox, both types of hours are of equal length.) An equinoctial hour is one of the 24 equal parts of the full day (which includes daytime and nighttime).
The time of day is typically expressed in English in terms of hours. Whole hours on a 12-hour clock are expressed using the contracted phrase o'clock, from the older of the clock. [6] (10 am and 10 pm are both read as "ten o'clock".) Hours on a 24-hour clock ("military time") are expressed as "hundred" or "hundred hours".
The daytime canonical hours of the Catholic Church take their names from the Roman clock: the prime, terce, sext and none occur during the first (prīma) = 6 am, third (tertia) = 9 am, sixth (sexta) = 12 pm, and ninth (nōna) = 3 pm, hours of the day. The English term noon is also derived from the ninth hour.
The Ohio Clock in the U.S. Capitol being turned forward for the country's first daylight saving time on March 31, 1918 by the Senate sergeant at arms Charles Higgins.. Most of the United States observes daylight saving time (DST), the practice of setting the clock forward by one hour when there is longer daylight during the day, so that evenings have more daylight and mornings have less.
Huygens first used a clock to calculate the equation of time (the difference between the apparent solar time and the time given by a clock), publishing his results in 1665. The relationship enabled astronomers to use the stars to measure sidereal time , which provided an accurate method for setting clocks.
(The leading zero is more commonly used with the 24-hour notation; especially in computer applications because it can help to maintain column alignment in tables and correct sorting order, and also because it helps to highlight the 24-hour character of the given time.) Times of day ending in :00 minutes may be pronounced as the numbered hour ...