abstract:Barycentric Dynamical Time (TDB) is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilationExplanations given with (a) IAU resolutions 1991, under Resolution A.4, at 'Notes for recommendation III', and IAU 2006 resolution 3, and its footnotes; and (b) explanations and references cited at "Time dilation -- due to gravitation and motion together".