Calendars and time
Barycentric Coordinate Time
Direct answer
Barycentric Coordinate Time: Barycentric Coordinate Time, or TCB, is the relativistic coordinate time of the solar-system barycentric reference system.
TCB is the coordinate time used in the solar-system barycentric frame.
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At a glance
- Found in
- Calendars & Timekeeping
- Related
- Barycentric Dynamical Time, Geocentric Coordinate Time, Calendar, Julian Date
TCB is the coordinate time used in the solar-system barycentric frame.
A cycle or timeline schematic for comparing the named timekeeping concept.
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The story behind Barycentric Coordinate Time
The IAU defined TCB in 1991 as part of a coherent relativistic framework for astronomical reference systems.
Why Barycentric Coordinate Time matters
Barycentric Coordinate Time provides a consistent independent variable for relativistic equations whose origin is at the solar-system barycenter.
How to read Barycentric Coordinate Time
TCB in high-precision astrometry and dynamical theory applies when the barycentric coordinate system is explicit.
Barycentric Coordinate Time in practice: an example
TCB advances at a different mean rate from geocentric TT because the coordinate potentials and motions differ.
Where readings of Barycentric Coordinate Time go wrong
The usual misreading is to compare TCB numeric values directly with UTC or TT without the prescribed transformation.
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
Work in the barycentric frame
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More in Calendars & Timekeeping
- Civil Day
- DUT1
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- ISO Week Date
- Lunar Calendar
- Proleptic Julian Calendar
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Common questions
What is Barycentric Coordinate Time?
Barycentric Coordinate Time, or TCB, is the relativistic coordinate time of the solar-system barycentric reference system.
What do people get wrong about Barycentric Coordinate Time?
The usual misreading is to compare TCB numeric values directly with UTC or TT without the prescribed transformation.
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