Barycentric Dynamical Time

Barycentric Dynamical Time
TDG
Tidal Dwarf Galaxy. A self-gravitating entity of dwarf-galaxy mass, built from tidal material expelled during interactions. Examples include AM0547-244, AM1054-325 and AM1353-272 (see Weilbacher, et al.

Barycentric Dynamical Time (TDB). Differing from TDT only via periodic variations, TDB is used in ephemerides and equations of motion that refer to the barycenter of the solar system.

As the theoretical basis for Ephemeris Time is wholly non-relativistic, in 1976 the IAU resolved that beginning in 1984 ET would be replaced by the two relativistic timescales Barycentric Dynamical Time (TDB) and Terrestrial Dynamical Time (TDT).

The center of mass of a system of bodies; e.g., the center of mass of the solar system or the Earth-Moon system. [S92]
Barycentric Dynamical Time (TDB) ...

DT has two expressions, Terrestrial Time, TT, (or Terrestrial Dynamical Time, TDT), and Barycentric Dynamical Time, TDB. More information on these, and still more timekeeping expressions, may be found at the U.S. Naval Observatory website.

In 1984 ephemeris time was renamed terrestrial dynamical time (TDT or TT); also created was barycentric dynamical time (TDB), which is based on the orbital motion of the sun, moon, and planets.

See also: Time, Earth, Solar, Orbit, Planet