ΔT (timekeeping) - определение. Что такое ΔT (timekeeping)
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Что (кто) такое ΔT (timekeeping) - определение

MEASURE OF VARIATION OF SOLAR TIME FROM ATOMIC TIME
Difference between Terrestrial Time (TT) and Universal Time (UT1); Length of day (astronometry)
  • Δ''T'' vs. time from 1657 to 2022<ref>IERS Rapid Service/Prediction Center (c. 1986). [http://maia.usno.navy.mil/ser7/historic_deltat.data ''Historic Delta T and LOD'']. Source attributed data to McCarthy and Babcock (1986). Retrieved April 2022.</ref><ref>IERS Rapid Service/Prediction Center. [http://maia.usno.navy.mil/ser7/deltat.data ''Delta T determinations'']. Retrieved April 2022.</ref>

ΔT (timekeeping)         
In precise timekeeping, ΔT (Delta T, delta-T, deltaT, or DT) is a measure of the cumulative effect of the departure of the Earth's rotation period from the fixed-length day of International Atomic Time (86,400 seconds). Formally, ΔT is the time difference between Universal Time (UT, defined by Earth's rotation) and Terrestrial Time (TT, independent of Earth's rotation).
History of timekeeping devices         
  • The [[Tower of the Winds]] in Athens (1st&nbsp;century&nbsp;BC)
  • Allegory of Good Government]]'' ({{circa}} 1338)
  • National Physical Laboratory]] in London
  • An [[incense clock]]; time was measured by means of powdered incense burnt along a pre-measured path
  • Detail from the face of an [[equation clock]] made by [[Ferdinand Berthoud]], {{circa}}1752 ([[Metropolitan Museum of Art]])
  • Treatise of statics and mechanics]]'
  • chronometer]]
  • [[Engraving]] of [[John Harrison]]—with his [[gridiron pendulum]] shown in the background (1768), [[Science Museum, London]]
  • An Ancient Egyptian [[sundial]] ([[Rijksmuseum van Oudheden]])
  • A detail of the [[Salisbury Cathedral clock]], showing the [[verge and foliot]]
  • Water clock (representing a clock at the royal court in Paris, {{circa}}1250)
  • The so-called 'Henlein Watch'
HISTORY OF DEVICES FOR MEASURING TIME
Timeline of time measurement technology; History of timekeepinig; Wrist watch (history); History of time keeping; History of clocks; History of timekeeping; History of timekeeping instruments; Time and measurement; History of timepieces; Precision timekeeping; Era of precision timekeeping
The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have since then improved through a long series of new inventions and ideas.
History of timekeeping devices in Egypt         
ASPECT OF HISTORY
The ancient Egyptians were one of the first cultures to widely divide days into generally agreed-upon equal parts, using early timekeeping devices such as sundials, shadow clocks, and merkhets (plumb-lines used by early astronomers).

Википедия

ΔT (timekeeping)

In precise timekeeping, ΔT (Delta T, delta-T, deltaT, or DT) is a measure of the cumulative effect of the departure of the Earth's rotation period from the fixed-length day of International Atomic Time (86,400 seconds). Formally, ΔT is the time difference ΔT = TT − UT between Universal Time (UT, defined by Earth's rotation) and Terrestrial Time (TT, independent of Earth's rotation). The value of ΔT for the start of 1902 was approximately zero; for 2002 it was about 64 seconds. So Earth's rotations over that century took about 64 seconds longer than would be required for days of atomic time. As well as this long-term drift in the length of the day there are short-term fluctuations in the length of day (Δτ) which are dealt with separately.

Since 2017, the length of the day has happened to be very close to the conventional value, and ΔT has remained within a second of 69 seconds