TDBTT Subroutine

public subroutine TDBTT(tdb1, tdb2, dtr, tt1, tt2, j)

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

Status: canonical.

Notes

1. TDB1+TDB2 is Julian Date, apportioned in any convenient way between the two arguments, for example where TDB1 is the Julian Day Number and TDB2 is the fraction of a day. The returned TT1,TT2 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 SOFA routine DTDB. 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

History

• IAU SOFA revision: 2019 June 20

Arguments

    subroutine TDBTT ( tdb1, tdb2, dtr, tt1, tt2, j )

    implicit none

    real(wp),intent(in) :: tdb1 !! TDB as a 2-part Julian Date
    real(wp),intent(in) :: tdb2 !! TDB as a 2-part Julian Date
    real(wp),intent(in) :: dtr !! TDB-TT in seconds
    real(wp),intent(out) :: tt1 !! TT as a 2-part Julian Date
    real(wp),intent(out) :: tt2 !! TT as a 2-part Julian Date
    integer,intent(out) :: j !! status:  0 = OK

    real(wp) :: dtrd

    !  Result, safeguarding precision.
    dtrd = dtr/d2s
    if ( abs(tdb1)>abs(tdb2) ) then
       tt1 = tdb1
       tt2 = tdb2 - dtrd
    else
       tt1 = tdb1 - dtrd
       tt2 = tdb2
    end if

    !  Status (always OK).
    j = 0

    end subroutine TDBTT