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# tttdb

erfa.tttdb(tt1, tt2, dtr)

  Time scale transformation: Terrestrial Time, TT, to Barycentric Dynamical Time, TDB.

  Parameters:
    tt1 double array
    tt2 double array
    dtr double array
  Returns:
    tdb1 double array
    tdb2 double array

  Notes

  Wraps ERFA function `eraTttdb`. The ERFA documentation is:

      - - - - - - - - -
       e r a T t t d b
      - - - - - - - - -

      Time scale transformation:  Terrestrial Time, TT, to Barycentric
      Dynamical Time, TDB.

      Given:
         tt1,tt2    double    TT as a 2-part Julian Date
         dtr        double    TDB-TT in seconds

      Returned:
         tdb1,tdb2  double    TDB as a 2-part Julian Date

      Returned (function value):
                    int       status:  0 = OK

      Notes:

      1) tt1+tt2 is Julian Date, apportioned in any convenient way between
         the two arguments, for example where tt1 is the Julian Day Number
         and tt2 is the fraction of a day.  The returned tdb1,tdb2 follow
         suit.

      2) The argument dtr represents the quasi-periodic component of the
         GR transformation between TT and TCB.  It is dependent upon the
         adopted solar-system ephemeris, and can be obtained by numerical
         integration, by interrogating a precomputed time ephemeris or by
         evaluating a model such as that implemented in the ERFA function
         eraDtdb.   The quantity is dominated by an annual term of 1.7 ms
         amplitude.

      3) TDB is essentially the same as Teph, the time argument for the JPL
         solar system ephemerides.

      References:

         McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
         IERS Technical Note No. 32, BKG (2004)

         IAU 2006 Resolution 3

      This revision:  2021 May 11

      Copyright (C) 2013-2023, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.