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The farthest time from midnight was 17 minutes in 1991, and the nearest is 90 seconds, set on January 2023. The clock was moved to 150 seconds (2 minute, 30 seconds) in 2017, then forward to 2 minutes to midnight in January 2018, and left unchanged in 2019. [ 5 ]
The length of the SI second was calibrated on the basis of the second of ephemeris time [29] [32] and can now be seen to have a relationship with the mean solar day observed between 1750 and 1892, analysed by Simon Newcomb. As a result, the SI second is close to 1 / 86400 of a mean solar day in the mid‑19th century. [44]
Universal Time ( UT or UT1) is a time standard based on Earth's rotation. [ 1] While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle ...
Timeline for the day of the September 11 attacks. The hijacked United Airlines Flight 175 approaching the South Tower (left) as the North Tower (right) burns next to it. The September 11 attacks of 2001, in addition to being a unique act of terrorism, constituted a media event on a scale not seen since the advent of civilian global satellite links.
The Uniform Time Act of 1966 established a uniform set of rules for states opting to observe daylight saving time. [ 1] In the U.S., daylight saving time starts on the second Sunday in March and ends on the first Sunday in November, with the time changes taking place at 2:00 a.m. local time. With a mnemonic word play referring to seasons ...
International Atomic Time. International Atomic Time (abbreviated TAI, from its French name temps atomique international [1]) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid. [2] TAI is a weighted average of the time kept by over 450 atomic clocks in over 80 national laboratories ...
Animation showing the difference between a sidereal day and a solar day. Sidereal time ("sidereal" pronounced / saɪˈdɪəriəl, sə -/ sy-DEER-ee-əl, sə-) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky.
The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each (24 × 60 × 60 = 86400). "Minute" comes from the Latin pars minuta prima, meaning "first ...