Coordinated Universal Time (UTT)
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International time system for civil and scientific use, implemented in 1963, abbreviated UTC. It is based on one second measured by atomic clocks and is widely broadcast by radio signals. These signals are used to synchronize all public and private clocks. Since January 1, 1972, it has been adjusted by adding leap seconds as necessary. UTC is based on atomic time, which is based on atomic clocks, but is adjusted for the difference between atomic time and UT1, which is a solar time corrected by astronomical measurements of the Earth's rotation, and is kept within ±0.9 seconds of UT1. The difference from International Atomic Time (TAI) is always an integer number of seconds. Because the Earth's rotation speed slows irregularly due to tidal friction and other forces, the solar year currently has about one more second measured by atomic clocks than UT1. Leap seconds are therefore added to UTC as necessary, such as making the last minute of December or June 61 seconds long. The insertion of a leap second will be announced at least eight weeks in advance by the International Earth Rotation Observatory of the Paris Observatory. (→Time, Universal Time) Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
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常用および科学分野で使われる国際的時法。1963年実施。略記 UTC。原子時計が刻む 1秒を基準単位とし，電波信号によって広く配信される。この電波があらゆる公的，私的な時計を合わせるのに用いられている。1972年1月1日以降，必要に応じ閏秒を加えて調整されている。UTCは, 原子時計を元にした原子時に基づきながら，原子時と，地球の自転の天文測定値から算出される太陽時を補正した UT1との間に生じる時間差を調整したもので，UT1から±0.9秒の範囲内に保たれている。国際原子時 TAIとの差は常に整数秒である。地球の自転速度は潮汐摩擦やその他の力によって不規則に遅くなるため，現在，1太陽年は原子時計の秒で刻むと，UT1の秒数より約 1秒多い。そのため 12月または 6月の最終の 1分を 61秒とするなど，必要に応じて UTCに閏秒が加えられる。閏秒の挿入は，パリ天文台の国際地球回転観測事業により少なくとも 8週間前に発表される。（→時間，世界時）
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