Book contents
- Time: From Earth Rotation to Atomic Physics
- Time: From Earth Rotation to Atomic Physics
- Copyright page
- Dedication
- Contents
- Preface
- 1 Time Before the 20th Century
- 2 Time from the Earth’s Rotation
- 3 Ephemerides
- 4 Variable Earth Rotation
- 5 Earth Orientation
- 6 Ephemeris Time
- 7 Relativity and Time
- 8 Time and Cosmology
- 9 Dynamical and Coordinate Timescales
- 10 Clock Developments
- 11 Microwave Atomic Clocks
- 12 Optical Atomic Standards
- 13 Definition and Role of a Second
- 14 International Atomic Time (TAI)
- 15 Coordinated Universal Time (UTC)
- 16 Time in the Solar System
- 17 Time and Frequency Transfer
- 18 Modern Earth Orientation
- 19 International Activities
- 20 Time Applications
- 21 Future of Timekeeping
- Acronyms
- Glossary
- Index
- References
6 - Ephemeris Time
Published online by Cambridge University Press: 01 October 2018
Book contents
- Time: From Earth Rotation to Atomic Physics
- Time: From Earth Rotation to Atomic Physics
- Copyright page
- Dedication
- Contents
- Preface
- 1 Time Before the 20th Century
- 2 Time from the Earth’s Rotation
- 3 Ephemerides
- 4 Variable Earth Rotation
- 5 Earth Orientation
- 6 Ephemeris Time
- 7 Relativity and Time
- 8 Time and Cosmology
- 9 Dynamical and Coordinate Timescales
- 10 Clock Developments
- 11 Microwave Atomic Clocks
- 12 Optical Atomic Standards
- 13 Definition and Role of a Second
- 14 International Atomic Time (TAI)
- 15 Coordinated Universal Time (UTC)
- 16 Time in the Solar System
- 17 Time and Frequency Transfer
- 18 Modern Earth Orientation
- 19 International Activities
- 20 Time Applications
- 21 Future of Timekeeping
- Acronyms
- Glossary
- Index
- References
Summary
The discovery of the variability of the Earth's rotation rate called for a uniform timescale for ephemerides and other scientific purposes. André Danjon and Gerald Clemence proposed a timescale based on the orbital motion of the Earth that was adopted in 1952, and called Ephemeris Time (ET). The working definition was based on a mathematical expression for the longitude of the Sun as a function of time. However, observations of the Sun are difficult and limited in accuracy, so observations of the Moon were used in practice to determine Ephemeris Time. This time depended on the analysis of astronomical observations. Consequently, it was not available immediately. Fortunately, atomic clocks started to become available in 1956, providing a timescale accurately representing ET. The availability of atomic timescales led to the introduction of International Atomic Time (TAI) and dynamical timescales.
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- Information
- Time: From Earth Rotation to Atomic Physics , pp. 88 - 103Publisher: Cambridge University PressPrint publication year: 2018
References
BIPM Com. Cons. Déf. Seconde (1970). 5, 21–23. Reprinted in B. E. Blair, ed., Time and Frequency: Theory and Fundamentals, Natl. Bur. Stand. (U.S.) Monograph 140, Washington, DC: US Government Printing Office.Google Scholar
Brouwer, D. (1952). A Study of the Changes in the Rate of Rotation of the Earth. Astron. J., 57, 125–146.CrossRefGoogle Scholar
Brown, E. W. (1897–1908). Theory of the Motion of the Moon. Containing a New Calculation of the Expressions for the Coordinates of the Moon in Terms of the Time. Mem. R. Astron. Soc., 53, 39–116, 163–202; 54, 1–63; 57, 51–145; 59, 1–103.Google Scholar
Clemence, G. M. (1948). On the System of Astronomical Constants. Astron. J, 53, 169–179.Google Scholar
Clemence, G. M. (1971). The Concept of Ephemeris Time: A Case of Inadvertent Plagiarism. J. History of Astronomy, 2, 73–79.CrossRefGoogle Scholar
Colloque sur le gravitationnel problème des n corps. Paris, France, 16–18 Août, 1967. (Conference on the Gravitational N-Body Problem, Paris, France, August 16–18, 1967) (1968). Paris, Publication du Centre National de la Recherche Scientifique.Google Scholar
Colloque international sur les constantes fondamentales de l’astronomie (1950). In Bull. Astron., 15, 163–292.Google Scholar
Danjon, A. (1929). Le temps, sa définition pratique, sa mesure. L’astronomie, 43, 13–22.Google Scholar
Essen, L. & Perry, J. V. L. (1957). The Cesium Resonator as a Standard of Frequency and Time. Phil. Trans R. Soc. London Series A, 250, 45–69.Google Scholar
Fricke, W., Kopff, A., in collaboration with Gliese, W., Gondolatsch, F., Lederle, T., Nowacki, H., Strobel, W., & Stumpff, P. (1963). Fourth Fundamental Catalogue (FK4). Veröff. Astron. Rechen-Inst. Heidelberg, 10.Google Scholar
Fricke, W., Schwan, H., Lederle, T. in collaboration with Bastian, U., Bien, R., Burkhardt, G., du Mont, B., Hering, R., Jährling, R., Jahreiß, H., Röser, S., Schwerdtfeger, H. M., & Walter, H. G. (1988). Fifth Fundamental Catalogue (FK5). Part I. The Basic Fundamental Stars. Veröff. Astron. Rechen-Inst. Heidelberg, 32.Google Scholar
Improved Lunar Ephemeris 1952–1959 (1954). Washington, DC: US Government Printing Office.Google Scholar
Kaplan, G. H. (1982). The IAU Resolutions on Astronomical Constants, Time Scales, and the Fundamental Reference Frame. Washington, DC: US Naval Observatory Circular 163.Google Scholar
Markowitz, W. (1954). Photographic Determination of Moon’s Position, and Applications to the Measure of Time, Rotation of the Earth, and Geodesy. Astron. J., 59, 69–73.Google Scholar
Markowitz, W. (1961). The Photographic Zenith Tube and the Dual-Rate Moon-Position Camera. In Kuiper, G. P. & Middlehurst, B. M., eds., Telescopes, Stars and Stellar Systems. Chicago, IL: University of Chicago Press, 88.Google Scholar
Markowitz, W., Hall, R. G., Essen, L., & Perry, J. V. L. (1958). Frequency of Cesium in Terms of Ephemeris Time. Phys. Rev. Lett. 1, 105.Google Scholar
McCarthy, D. D. & Babcock, A. (1986). The Length of Day since 1656. Physics of the Earth and Planetary Interiors, 44, 281–292.Google Scholar
Morrison, L. V. & Stephenson, F. R. (2001). Historical Eclipses and the Variability of the Earth’s Rotation. J. Geodynamics, 32, 247–265.CrossRefGoogle Scholar
Morrison, L. V. & Stephenson, F. R. (2004). Historical Values of the Earth’s Clock Error ΔT and the Calculation of Eclipses. J. History of Astronomy, 35, 327–336.Google Scholar
Morrison, L. V. & Stephenson, F. R. (2005). ADDENDUM: Historical Values of the Earth’s Clock Error. J. History of Astronomy, 36, 339.Google Scholar
Mulholland, J. D. (1972). Measures of Time in Astronomy. Pub. Astron. Soc. Pacific, 94, 357–364.Google Scholar
Nelson, R. A., McCarthy, D. D., Malys, S., et al. (2001). The Leap Second: Its History and Possible Future. Metrologia, 38, 509–529.Google Scholar
Newcomb, S. (1895). Astronomical Papers of the American Ephemeris and Nautical Almanac, VI, Part I: Tables of the Sun. Washington, DC: US Government Printing Office, 9.Google Scholar
Spencer Jones, H. (1939). The Rotation of the Earth and the Secular Acceleration of the Sun, Moon, and Planets. Monthly Notices Roy. Astron. Soc., 99, 541.Google Scholar
Stephenson, F. R. (1997). Historical Eclipses and Earth’s Rotation. Cambridge, UK: Cambridge University Press.Google Scholar
Stephenson, F. R. (2003). Harold Jeffreys Lecture 2002: Historical Eclipses and Earth’s Rotation. Astronomy and Geophysics, 44, 2.22–2.27.Google Scholar
Stephenson, F. R. (2007a). Babylonian Timings of Eclipse Contacts and the Study of the Earth’s Past Rotation. J. History of Astronomy, 9, 145–150.Google Scholar
Stephenson, F. R. (2007b). Variations in the Earth’s Clock Error ΔT between AD 300 and 800 as Deduced from Observations of Solar and Lunar Eclipses. J. History of Astronomy, 10, 211–220.Google Scholar
Stephenson, F. R. & Morrison, L. V. (1984). Long-Term Changes in the Rotation of the Earth: 700 B.C. to A.D. 1980. In Hide, R., ed., Rotation in the Solar System (London, UK, 1984); reprinted in Phil. Trans. Royal Soc London, A, 313, 47–70.Google Scholar
Stephenson, F. R. & Morrison, L. V. (1994). Long-Term Changes in the Rotation of the Earth: 700 B.C. to A.D. 1990. Phil. Trans. Royal Soc London, A, 351, 165–202.Google Scholar
Stephenson, F. R., Morrison, L. V., & Hohenkerk, C. Y. (2016). Measurements of Earth Rotation 720 BC to AD 2015, Proceedings of Royal Society A, 472, 20160404.Google Scholar
Trans. Int. Astron. Union, Vol. VIII, Proc. 8th General Assembly, Rome, 1952. (1954). Oosterhoff, P. T., ed., New York, NY: Cambridge University Press, 66.Google Scholar
Trans. Int. Astron. Union, Vol. IX, Proc. 9th General Assembly, Dublin, 1955. (1957). Oosterhoff, P. T., ed., New York, NY: Cambridge University Press, 451.Google Scholar
Trans. Int. Astron. Union, Vol. X B, Proc. 10th General Assembly, Moscow, 1958. (1960). Sadler, D. H., ed. Cambridge, UK: Cambridge University Press.Google Scholar
Watts, C. B. (1963). The Marginal Zone of the Moon. Astronomical Papers for the American Ephemeris and Nautical Almanac, vol. 17. Washington, DC: US Government Printing Office.Google Scholar
Will, C. M. (1974). Experimental Gravitation, Bertotti, B. ed. New York, NY: Academic Press.Google Scholar
Williams, J. G. & Boggs, D. H. (2016). Secular Tidal Changes in Lunar Orbit and Earth Rotation. Celest. Mech. & Dynam. Astron., 126, 88–129.Google Scholar