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The definition of time and different time systems
Published in Lucien Wald, Fundamentals of Solar Radiation, 2021
The speed of rotation of the Earth on itself is not constant. High-frequency irregularities in speed occur due to the displacement of air and water masses, or even to earthquakes. They are unpredictable, and this makes impossible a very accurate definition of time based solely on this rotation, and therefore on UT1. The international atomic time is used to smooth the variations due to irregularities in rotation, as it sets the frequencies of time, like the second. This yields the coordinated universal time, curiously abbreviated as UTC.
The Earth–Sun Relationship
Published in Matt Fajkus, Dason Whitsett, Architectural Science and the Sun, 2018
In an effort to alleviate this confusion, in 1878, Sir Sanford Fleming proposed the establishment of time zones (TZ) within which there would be only one local standard time. The Royal Observatory at Greenwich, England, was declared the basis for measurement of time, with the creation of Greenwich Mean Time (GMT). GMT has since been superseded by coordinated universal time (UTC) as the standard for time keeping. For most practical purposes, GMT and UTC are the same, but UTC should be used to avoid confusion. Each time zone is offset by a given increment ahead of or behind UTC. For example, UTC +5 indicates local standard time is 5 hours ahead of UTC 0 (formerly Greenwich Mean Time). The Earth rotates 15° on its axis each hour, turning a full 360° rotation in 24 hours. Therefore, to establish time zones with increments of one hour, reference meridians known as local standard meridians (LSM) occur every 15° of longitude in each direction from the prime meridian. The area from 7.5° west to 7.5° east of the local standard meridian theoretically falls into that one-hour time zone.
Time Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Coordinated Universal Time (UTC) is an atomic time scale that is based on the SI definition of the second and that serves as the official time reference for most of the world. UTC is maintained by the Bureau International des Poids et Mesures (BIPM) in Sevres, France. As of 2010, it is computed from a weighted average of nearly 400 atomic standards located at some 70 laboratories, including the National Institute of Standards and Technology (NIST) and the US Naval Observatory (USNO). Most of these devices are cesium beam standards, but some are hydrogen masers. In addition, about ten cesium fountain standards contribute to the accuracy of UTC.
Clock synchronisation: the establishment of Coordinated Universal Time (UTC) through the work of Louis Essen
Published in The International Journal for the History of Engineering & Technology, 2023
Markowitz agreed to send his results to Smith who decided whether to adjust the clocks that controlled GMT at the Royal Greenwich Observatory on the basis of the combined Anglo-American astronomical observations. A cablegram to Markowitz – sent via the British Embassy in Washington D.C. – allowed the US and UK to act in concert in sending out their time signals at the same moment. The scheme worked well and an expanded arrangement was formally implemented on 1 January 1960 when the Naval Observatory, National Bureau of Standards and Naval Research Laboratory in America and the National Physical Laboratory and the Royal Greenwich Observatory in Britain began to coordinate their radio time signals. Beginning with this effort, standard time on the prime meridian was designated ‘UTC’ (Coordinated Universal Time) and this became the common time scale adopted by all of the participating laboratories.57
Constant-level spatio-temporal integrated search algorithm for repeating sun-synchronous orbit satellite images
Published in International Journal of Digital Earth, 2021
Each Landsat 8 scene has a metadata file containing its spatial coverage and temporal information. The temporal information includes the acquisition date, beginning time (the corresponding time when the scene starts to be recorded), end time (the corresponding time when the recording ends), and product generated date. The time information is defined in Coordinated Universal Time (UTC) and local time. The spatial information includes the coordinates of the four corners and the center of the scene and the corresponding path and row numbers.