The Development of Coordinated Universal Time

Dennis D. McCarthy

Abstract: In the nineteenth century the words "universal time" referred only to the concept of a time scale that might be the same all over the world, as opposed to the numerous "local time" scales. In the eighteenth century Greenwich Mean Time was one of a small number of time scales to be used in conjunction with national almanacs for navigational purposes, but in 1884, following a number of international meetings, the International Meridian Conference proposed the Greenwich meridian as the origin of longitudes and further proposed the adoption of a "universal day" as the basis for timekeeping. This led to the use of the names Greenwich Mean Time, Greenwich Civil Time and Greenwich Mean Astronomical Time. In 1928 the International Astronomical Union first recommended using the name "Universal Time" to refer to the mean solar time on the Greenwich meridian. By 1956 astronomers recognized three varieties of Universal Time based on observations of stars, and by 1960 the term "Coordinated Universal Time" was being used informally to refer to the practice of timekeeping laboratories to "coordinate" their adjustments to clocks based on astronomical observations. The name was formalized by the Consultative Committee on Radio Communications (CCIR) in 1963, and in 1967 the CCIR and the IAU officially adopted the names Coordinated Universal Time and Temps Universel Coordonné (UTC). During all that time the science of timekeeping improved by orders of magnitude proceeding from a time scale based solely on stellar observations to one based on the frequency of an atomic transition in the Caesium atom. The development of UTC continues today with existing speculation regarding its definition, practical realization and applications.
Published in: Proceedings of the 50th Annual Precise Time and Time Interval Systems and Applications Meeting
January 28 - 31, 2019
Hyatt Regency Reston
Reston, Virginia
Pages: 8 - 52
Cite this article: McCarthy, Dennis D., "The Development of Coordinated Universal Time," Proceedings of the 50th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, January 2019, pp. 8-52.
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