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An hour (symbol: h; [1] also abbreviated hr) is a unit of time historically reckoned as 1 ⁄ 24 of a day and defined contemporarily as exactly 3,600 seconds . There are 60 minutes in an hour, and 24 hours in a day. The hour was initially established in the ancient Near East as a variable measure of 1 ⁄ 12 of the night or daytime.
A day is the time period of a full rotation of the Earth with respect to the Sun.On average, this is 24 hours (86,400 seconds).As a day passes at a given location it experiences morning, afternoon, evening, and night.
Earth-based: the day is based on the time it takes for the Earth to rotate on its own axis, as observed on a sundial [citation needed]. Units originally derived from this base include the week (seven days), and the fortnight (14 days). Subdivisions of the day include the hour (1/24 of a day), which is further subdivided into minutes and seconds ...
24-hour digital clock in Miaoli HSR station. A public 24-hour clock in Curitiba, Brazil, with the hour hand on the outside and the minute hand on the inside.. A time of day is written in the 24-hour notation in the form hh:mm (for example 01:23) or hh:mm:ss (for example, 01:23:45), where hh (00 to 23) is the number of full hours that have passed since midnight, mm (00 to 59) is the number of ...
Times relative to the designation are indicated with +/−[Arabic numeral] after the letter, replacing -day or -hour with a count of the same unit: "D−1" (the day before D-Day), "L+9" (9 hours after L-Hour) etc. [citation needed] In less formal contexts, the symbol or numeral may be spelled out: "D minus 1" or "L plus nine." [citation needed ...
The natural day (dies naturalis) ran from sunrise to sunset. [6] The hours were numbered from one to twelve as hora prima, hora secunda, hora tertia, etc. To indicate that it is a day or night hour, Romans used expressions such as for example prima diei hora (first hour of the day), and prima noctis hora (first hour of the night). [7]
kè has been defined as 1 ⁄ 96 of a day since 1628, so the modern kè equals 15 minutes and each double hour contains exactly 8 kè. [2] Since then, kè has been used as shorthand to talk about time in 1 ⁄ 8 of a double hour or 1 ⁄ 4 of a single hour. Their usage is similar to using "quarter hour" for 15 minutes or "half an hour" for 30 ...
One kè was usually defined as 1 ⁄ 100 of a day until 1628, though there were short periods before then where days had 96, 108 or 120 kè. [7] A kè is about 14.4 minutes, or 14 minutes 24 seconds. In the 19th century, Joseph Charles François de Rey-Pailhade endorsed Lagrange’s proposal of using centijours, but abbreviated cé , and ...