Calendars and time
Barycentric Dynamical Time
Direct answer
Barycentric Dynamical Time: Barycentric Dynamical Time, or TDB, is a time scale for solar-system barycentric calculations designed to remain close to Terrestrial Time on average.
TDB is a barycentric ephemeris time scale kept near TT.
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At a glance
- Found in
- Calendars & Timekeeping
- Related
- Dynamical Time, Barycentric Coordinate Time, Calendar, Julian Date
TDB is a barycentric ephemeris time scale kept near TT.
A cycle or timeline schematic for comparing the named timekeeping concept.
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The story behind Barycentric Dynamical Time
The IAU refined TDB definition after earlier dynamical-time terminology created ambiguity in relativistic calculations.
Why Barycentric Dynamical Time matters
Barycentric Dynamical Time supports relativistic solar-system dynamics without the long-term rate difference that unscaled barycentric coordinate time has from TT.
How to read Barycentric Dynamical Time
TDB for planetary ephemerides, spacecraft light-time work, and barycentric corrections applies when the data standard specifies it.
Barycentric Dynamical Time in practice: an example
A pulsar photon arrival time may be converted from a spacecraft clock to a TDB value at the solar-system barycenter.
Where readings of Barycentric Dynamical Time go wrong
It is a mistake to substitute TT for TDB when microsecond-level barycentric timing matters.
Sources and editorial method
Research references used for this entry include:
- IAU SOFA: Time Scale and Calendar Tools - IAU-standard algorithms and guidance for civil calendars, Julian dates, and seven recognized astronomical time scales.
- U.S. Naval Observatory Circular 179: The IAU Resolutions on Astronomical Reference Systems, Time Scales, and Earth Rotation Models - Technical reference for TAI, TT, TCG, TCB, TDB, UT1, sidereal time, epochs, and Earth rotation.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Use the barycentric time argument
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More in Calendars & Timekeeping
- Common Era
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- Julian Calendar
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Common questions
What is Barycentric Dynamical Time?
Barycentric Dynamical Time, or TDB, is a time scale for solar-system barycentric calculations designed to remain close to Terrestrial Time on average.
What do people get wrong about Barycentric Dynamical Time?
It is a mistake to substitute TT for TDB when microsecond-level barycentric timing matters.
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