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# tcbtdb

erfa.tcbtdb(tcb1, tcb2)

  Time scale transformation: Barycentric Coordinate Time, TCB, to Barycentric Dynamical Time, TDB.

  Parameters
    tcb1 double array
    tcb2 double array
  Returns
    tdb1 double array
    tdb2 double array

  Notes

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

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

      Time scale transformation:  Barycentric Coordinate Time, TCB, to
      Barycentric Dynamical Time, TDB.

      Given:
         tcb1,tcb2  double    TCB as a 2-part Julian Date

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

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

      Notes:

      1) tcb1+tcb2 is Julian Date, apportioned in any convenient way
         between the two arguments, for example where tcb1 is the Julian
         Day Number and tcb2 is the fraction of a day.  The returned
         tdb1,tdb2 follow suit.

      2) The 2006 IAU General Assembly introduced a conventional linear
         transformation between TDB and TCB.  This transformation
         compensates for the drift between TCB and terrestrial time TT,
         and keeps TDB approximately centered on TT.  Because the
         relationship between TT and TCB depends on the adopted solar
         system ephemeris, the degree of alignment between TDB and TT over
         long intervals will vary according to which ephemeris is used.
         Former definitions of TDB attempted to avoid this problem by
         stipulating that TDB and TT should differ only by periodic
         effects.  This is a good description of the nature of the
         relationship but eluded precise mathematical formulation.  The
         conventional linear relationship adopted in 2006 sidestepped
         these difficulties whilst delivering a TDB that in practice was
         consistent with values before that date.

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

      Reference:

         IAU 2006 Resolution B3

      This revision:  2021 May 11

      Copyright (C) 2013-2021, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.