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| Barycentric Dynamical Time | |
|---|---|
| Name | Barycentric Dynamical Time |
| Abbreviation | TDB |
| Introduced | 1976 (redefined 2006) |
| Predecessor | Ephemeris Time, Terrestrial Time |
| Usage | Astronomical ephemerides, spacecraft navigation |
| Realization | Barycentric Coordinate Time corrections to Terrestrial Time |
Barycentric Dynamical Time Barycentric Dynamical Time is a relativistic time coordinate used for computing positions and motions of bodies in the Solar System, enabling consistent ephemerides and navigation; it interfaces with observational systems and spacecraft operations while accounting for effects predicted by Albert Einstein's theory of General relativity, the dynamics underlying the Solar System modeled by the International Astronomical Union, and practical realizations tied to terrestrial standards like International Atomic Time and Coordinated Universal Time. TDB provides a uniform time argument for dynamical equations that govern the motion of planets and minor bodies, supporting missions by agencies such as National Aeronautics and Space Administration, European Space Agency, and observatories like the Jet Propulsion Laboratory and the European Southern Observatory.
Barycentric Dynamical Time serves as the barycentric coordinate time for dynamical models referenced to the barycenter of the Solar System, intended to be free of periodic terms tied to Earth's orbital motion and usable in the equations of motion used by groups such as the International Astronomical Union and the International Earth Rotation and Reference Systems Service, facilitating computations by institutions including the Jet Propulsion Laboratory, Harvard–Smithsonian Center for Astrophysics, and the Max Planck Institute for Solar System Research. It is defined to align with relativistic frameworks developed by Hermann Minkowski and Albert Einstein and to be consistent with celestial reference frames maintained by the International Celestial Reference Frame custodians and the International Astronomical Union. The purpose includes providing a time argument for ephemerides produced by teams at Jet Propulsion Laboratory, Institute of Applied Astronomy, and the United States Naval Observatory.
The conceptual lineage of TDB traces through Ephemeris Time introduced under guidance from astronomers such as W. M. Smart and administered by observatories like Royal Greenwich Observatory and agencies including the International Astronomical Union; the need for a relativistic barycentric time scale became acute during the rise of precision radar ranging and spacecraft navigation led by NASA and the Soviet space program. Major milestones include the 1976 resolutions by the International Astronomical Union that formalized earlier dynamical time concepts, subsequent refinements influenced by work at Jet Propulsion Laboratory and the International Bureau of Weights and Measures, and the 2006 IAU adoption of modern relativistic time coordinate definitions influenced by researchers at Observatoire de Paris, Harvard University, and Max Planck Institute for Gravitational Physics. Developments were driven by collaborations among institutions like the European Space Agency, Russian Academy of Sciences, and the United States Naval Observatory.
TDB is realized as a coordinate time defined at the barycenter of the Solar System and is related to Terrestrial Time through relativistic transformations derived from the post-Newtonian formalism developed by theorists such as Clifford Will and implemented by groups at Jet Propulsion Laboratory and Observatoire de Paris. Practical realization uses numerical ephemerides created by teams at Jet Propulsion Laboratory (e.g., the DE series) and the Institute of Applied Astronomy (e.g., the EPM series), which supply tabulated corrections and polynomial approximations used by mission teams at European Space Agency, NASA, and the Russian Federal Space Agency. Implementations reference international standards maintained by the International Bureau of Weights and Measures and are incorporated into software by organizations such as Naval Observatory, European Space Operations Centre, and research centers like MIT and Caltech.
TDB is closely related to Terrestrial Time and Barycentric Coordinate Time through transformations required by General relativity, and its offsets and periodic terms are handled in comparison with International Atomic Time and Coordinated Universal Time for interoperability in operations run by NASA, European Space Agency, and observatories like Greenwich Observatory. The relation to Universal Time variants impacts astrometric reductions performed at institutions such as Royal Greenwich Observatory, US Naval Observatory, and Mount Wilson Observatory, while connections to specialized scales such as Geocentric Coordinate Time are critical for projects by European Space Agency and teams at Jet Propulsion Laboratory.
TDB is used in planetary and lunar ephemerides employed by mission planners at NASA Jet Propulsion Laboratory, trajectory designers at European Space Agency, and navigators at the United States Naval Observatory; it underpins orbit determination for spacecraft to destinations including Mars, Jupiter, and outer planets, and supports timing for pulsar timing arrays coordinated by centers like Harvard–Smithsonian Center for Astrophysics and Max Planck Institute for Radio Astronomy. Astronomical surveys conducted by institutions such as the European Southern Observatory, Sloan Digital Sky Survey, and space telescopes operated by European Space Agency and NASA rely on TDB-consistent ephemerides for astrometry, while fundamental astronomy research at Cambridge University and Princeton University employs TDB in dynamical modeling.
Precision and accuracy of TDB implementations depend on relativistic models developed by theorists like Clifford Will and computational ephemerides from Jet Propulsion Laboratory and Institute of Applied Astronomy, with residuals assessed by analysis teams at US Naval Observatory and Observatoire de Paris; corrections address periodic terms from Earth's orbital motion, solar gravitational potential modeled after studies at Max Planck Institute for Gravitational Physics, and tidal effects characterized by researchers at Scripps Institution of Oceanography and National Oceanic and Atmospheric Administration. Uncertainty budgets propagated in mission design by NASA and European Space Agency incorporate clock errors referenced to International Atomic Time and systematics characterized by laboratories such as National Institute of Standards and Technology and the International Bureau of Weights and Measures.
Notable realizations of TDB appear in the Jet Propulsion Laboratory DE ephemerides, the Institute of Applied Astronomy EPM series, and standards promulgated by the International Astronomical Union and the International Earth Rotation and Reference Systems Service, with software libraries supporting TDB transformations produced by organizations such as European Space Agency, NASA, US Naval Observatory, and academic groups at Harvard University and Caltech. Institutional adoption spans agencies including National Aeronautics and Space Administration, European Space Agency, Russian Federal Space Agency, and observatories like European Southern Observatory and Royal Greenwich Observatory, ensuring TDB's role in contemporary celestial mechanics, astrometry, and spacecraft navigation.
Category:Time scales