page_title: Hour
section_title: East Asia
hierarchical_section_title: Hour / History of timekeeping on other cultures / East Asia
caption_attribution_description: English: Replica Water Clock. Drum Tower, Beijing This is a replica of an ingenious Song dynasty clepsydra (water clock). Actually there was never water clock in the tower, so the replica here is simply a display piece for the modern visitor. The clock was regulated by the flow of water between the three buckets arranged in a "staircase" on top of the device. A cylinder, seen to the right, holds a level stick which indicated the time according to the water level inside the cylinder. The figure to the left, actuated by an overflow mechanism (tipping bucket), clashed its cymbals every quarter hour.
context_page_description: An hour is a unit of time conventionally reckoned as ​¹⁄₂₄ of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions. 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. Such seasonal, temporal, or unequal hours varied by season and latitude.
  Equal or equinoctial hours were taken as ​¹⁄₂₄ of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it ​¹⁄₂₄ of the mean solar day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second.
  In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. However, on rare occasions an hour may incorporate a positive or negative leap second, making it last 3,599 or 3,601 seconds, in order to keep it within 0.9 seconds of UT1, which is based on measurements of the mean solar day.
context_section_description: Ancient China divided its day into 100 "marks" (Chinese: 刻, oc *kʰək, p kè) running from midnight to midnight. The system is said to have been used since remote antiquity, credited to the legendary Yellow Emperor, but is first attested in Han-era water clocks and in the 2nd-century history of that dynasty. It was measured with sundials and water clocks. Into the Eastern Han, the Chinese measured their day schematically, adding the 20-ke difference between the solstices evenly throughout the year, one every nine days. During the night, time was more commonly reckoned during the night by the "watches" (Chinese: 更, oc *kæŋ, p gēng) of the guard, which were reckoned as a fifth of the time from sunset to sunrise.
  Imperial China continued to use ke and geng but also began to divide the day into 12 "double hours" (t 時, s 时, oc *də, p shí, lit. "time[s]") named after the earthly branches and sometimes also known by the name of the corresponding animal of the Chinese zodiac. The first shi originally ran from 11 pm to 1 am but was reckoned as starting at midnight by the time of the History of Song, compiled during the early Yuan. These apparently began to be used during the Eastern Han that preceded the Three Kingdoms era, but the sections that would have covered them are missing from their official histories; they first appear in official use in the Tang-era Book of Sui. Variations of all these units were subsequently adopted by Japan and the other countries of the Sinosphere.
  The 12 shi supposedly began to be divided into 24 hours under the Tang, although they are first attested in the Ming-era Book of Yuan. In that work, the hours were known by the same earthly branches as the shi, with the first half noted as its "starting" and the second as "completed" or "proper" shi. In modern China, these are instead simply numbered and described as "little shi". The modern ke is now used to count quarter-hours, rather than a separate unit.
  As with the Egyptian night and daytime hours, the division of the day into twelve shi has been credited to the example set by the rough number of lunar cycles in a solar year, although the 12-year Jovian orbital cycle was more important to traditional Chinese and Babylonian reckoning of the zodiac.
caption: A reconstruction of another kind of Chinese clepsydra in Beijing's Drum Tower
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