Editing Barycentric Dynamical Time (section)

==Use of TDB==

TDB is a successor of [[Ephemeris Time]] (ET), in that ET can be seen (within the limits of the lesser accuracy and precision achievable in its time) to be an approximation to TDB as well as to Terrestrial Time (TT) (see [[Ephemeris time#Implementations|Ephemeris time § Implementations]]). TDB in the form of the very closely analogous, and practically equivalent, time scale T<sub>eph</sub> continues to be used for the important DE405 planetary and lunar ephemerides from the [[Jet Propulsion Laboratory]].

Arguments have been put forward for the continued practical use of TDB rather than TCB based on the very small size of the difference between TDB and TT, not exceeding 0.002 second, which can be neglected for many applications. It has been argued that the smallness of this difference makes for a lower risk of damage if TDB is ever confused with TT, compared to the possible damage of confusing TCB and TT, which have a relative linear drift of about 0.5 second per year,<ref>S A Klioner (2008), "Relativistic scaling of astronomical quantities and the system of astronomical units", ''Astronomy and Astrophysics'', vol.478 (2008), pp.951-958, at page 953.</ref> (the difference was close to zero at the start of 1977, and by 2009 was already over a quarter of a minute and increasing).<ref name=timgraf />