Time(Jikan) or时(The sign:h) IsTime Ofunitone of. "International unit systemA unit that is used in combination with (SI) but does not belong to SI "(SI combination unit)^[1].. In addition, SI and JapanMeasurement LawThen, the name of the unit is only "hour", not "hour"^[2].

In Japanese,Times of DayaboutTimeIs used, and when referring to the time interval, it is usually "Time”Is used. Also in the same kanjiTimeThe word read as is a unit in the old Japanese hour system. See the section on indefinite time below.

One hour historically地球At 1Day(More accurately 1 averageSolar day) Has been defined as a 24 / 1th time interval. Currently, seconds are the basic unit of time, so one hour is defined as "1 times seconds." 3600 for 1 hourMinute.

Unit symbol Of h It is,1948The 9thInternational Weights and Measures General AssemblyIt was stipulated by Resolution 7 of (CGPM). Others such as hr may be used,International unit system(SI) and JapanMeasurement LawIn the system, only the symbol "h" is allowed and no other symbols may be used^[3].

History

The division of time used in ancient civilizations (Egypt, Mesopotamia, Indus, Yellow River) in various places issunriseAnd between sunset (or dawn and sunset)12Divide or divide the day by twice 124It was a divided item. 12 times 12144It wasn't a split. In any case, the split is a multiple of 12, which isMonth,directionIt has also been used for such purposes.

Until the definition of the current time was decided, the definition changed as follows.

Indefinite time method

Initially, 1/12 of the time from sunrise to sunset (or from dawn to sunset) is 1 hour (in Japan,1/6Was set to 1 o'clock (when). Therefore, the length varies greatly depending on the season, and one hour (1 o'clock) in the daytime is long in summer and short in winter. It also depends on the latitude, but this was not a problem while the range of human activity was narrow. At this timeIndefinite time methodThat is. In East Asia, the indefinite time method was used until the early modern period.

Fixed time method

Later, 1/24 of the visible solar day (between noon and the next noon, or between nightfall and the next nightfall) was set to 1 hour. This reduced the seasonal variation in hourly length, but the length of the solar day was still slightly different depending on the season, so it was necessary to adjust the clock several times a month.

after that,Average sun day1/24 of the time is now set to 1 hour. It seemed that the length of one hour was always constant,Rotation of the earthIs not constant, 10^-8orderIt was found that there was a fluctuation (about 1 to 86 milliseconds per day = 400 1 seconds), and this definition was no longer used. Regarding the transition of the definition and "length of day" after that,second,Leap second,Rotation of the earthchecking ...

Source

1. ^ Translation and supervision (Germany)National Institute of Advanced Industrial Science and Technology Metrology Standards Center "International Document 8th Edition (2006) International System of Units (SI) Japanese Edition(PDF), page 36.ISBN 92-822-2213-6.2016/4/12Browse. "Table 6 Non-SI Units Used with SI Units"
2. ^ Measurement Law Appendix XNUMX　"Time" column of the quantity of the state of the object
3. ^ Unit of Measure Regulations (November XNUMX, XNUMX Ministry of International Trade and Industry Ordinance No. XNUMX) Attached Table XNUMX (related to Article XNUMX) "Time" column Wikisource includesUnit of measure rule #AppendixThere is the original text of.

Related item

• Sun time
• Times of Day
• Time comparison
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• 1 hour race