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
9 - Dynamical and Coordinate Timescales
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
With the recognition of the problems with Ephemeris Time and the need to make changes in the celestial reference system in 1976, improved dynamical timescales continuous with Ephemeris Time and consistent with the theory of relativity were developed. Dynamical time is understood as the time-like argument of dynamical theories and the independent variable of the equations of motion of solar system bodies. In 1976, Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB) were introduced. Problems with the definition of TDT and TDB and the need for a new reference system based on accurate observations of distant radio sources were recognized. So Terrestrial Time (TT), Geocentric Coordinate Time (TCG), and Barycentric Coordinate Time (TCB) were introduced, and TDB was redefined. Barycentric Ephemeris Time (Teph) was officially recognized. Ephemeris Time Revised is still necessary for timescales prior to 1956. Relativistic equations specify the relationships between the different timescales.
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- Information
- Time: From Earth Rotation to Atomic Physics , pp. 131 - 147Publisher: Cambridge University PressPrint publication year: 2018
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