How old is the day of 24 equal hours?
Upvote:-2
Agreed with the 1st above comment.
The 24-hour time system has its origins in the Egyptian astronomical system of decans, which itself dates back to 10th Dynasty (2100 BCE).
There were 36 decans (36 X 10 = 360 days) and an additional 5 days to compose the 365 days of a solar year.
Eventually this system led to a system of 12 daytime hours and 12 nighttime hours, varying in length according to the season. Later, a system of 24 "equinoctial" hours was used.
References: - Neugebauer, Otto (1983) [1955]. "The Egyptian "Decans"". Astronomy and History: Selected Essays. New York: Springer. pp. 205–209. - Neugebauer, Otto (1969) [1957]. The Exact Sciences in Antiquity (2 ed.). Dover Publications. pp. 81–88.
Historical adoption:
1886: the Canadian Pacific Railway train at Port Arthur began using the 24-hour clock.
1893: Italy became the first to adopt the 24-hour clock nationally.
1909: The French Army began using the 24-hour clock while the rest of France did not start using this time system until 1912.
1915: The British Royal Navy began using this time system during the First World War and the Allied forces would follow suit as well.
1916: Denmark adopted the system.
1917: Greece adopted the system, along with the Canadian armed forces
1918: the British Army adopted the 24-hour clock.
1920: The United States Navy was the very first organization in the U.S.A. to utilize the 24-hour clock.
1920: Spain, Belgium, Portugal, and Switzerland finalized the switch, as most of the countries in Latin America.
1925: Turkey.
1927: Germany.
1942: US Army.
Upvote:21
Hipparchus, whose work primarily took place between 147 and 127 B.C., proposed dividing the day into 24 equinoctial hours, based on the 12 hours of daylight and 12 hours of darkness observed on equinox days. Despite this suggestion, laypeople continued to use seasonally varying hours for many centuries.
In terms of when the 24 hour day began to be relevant to ordinary people in their daily lives, my impression is that this would have come with advancements in mechanical clocks over the course of the Middle Ages and early modern period. See the history of timekeeping devices on Wikipedia, which states:
The appearance of clocks in writings of the 11th century implies that they were well known in Europe in that period. In the early 14th-century, the Florentine poet Dante Alighieri referred to a clock in his Paradiso; the first known literary reference to a clock that struck the hours.
However that article also points out with specific reference to sundials: "The idea of using hours of equal length throughout the year was the innovation of Abu'l-Hasan Ibn al-Shatir in 1371."
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