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Index Page deltet_c
Table of contents
Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       deltet_c ( Delta ET, ET - UTC )

       void deltet_c ( SpiceDouble      epoch,
                       ConstSpiceChar * eptype,
                       SpiceDouble    * delta )
#### Abstract
       Return the value of Delta ET (ET-UTC) for an input epoch.
#### Required_Reading
       TIME
       KERNEL
#### Keywords
       TIME
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       epoch      I   Input epoch (seconds past J2000).
       eptype     I   Type of input epoch ("UTC" or "ET").
       delta      O   Delta ET (ET-UTC) at input epoch.
#### Detailed_Input
       epoch       is the epoch at which "delta ET" is to be computed.
                   `epoch' may be either UTC or ephemeris seconds past
                   J2000, as specified by `eptype'.

       eptype      is the type of input epoch. It may be either
                   of the following:

                      "UTC"    UTC seconds past J2000 UTC.

                      "ET"     Ephemeris seconds past J2000 TDB,
                               also known as barycentric dynamical
                               time (TDB).
#### Detailed_Output
       delta       is the value of

                      "delta ET" = ET - UTC

                   at the input epoch. This is added to UTC to give
                   ET, or subtracted from ET to give UTC. The routine
                   is reversible: that is, given the following calls,

                      deltet_c ( utc,      "UTC", &del1 );
                      deltet_c ( utc+del1, "ET",  &del2 );

                   the expression

                      ( del1 == del2 )

                   is always SPICETRUE.
#### Parameters
       None.
#### Exceptions
       1)  If the input epoch is not recognized, the error
           SPICE(INVALIDEPOCH) is signaled by a routine in the call tree
           of this routine.

       2)  If the variables necessary for the computation of `delta' have
           not been loaded into the kernel pool, the error
           SPICE(KERNELVARNOTFOUND) is signaled by a routine in the call
           tree of this routine.

       3)  If the number of leapseconds in the pool is greater than the
           local leapseconds buffer size, the error SPICE(BUFFEROVERFLOW)
           is signaled by a routine in the call tree of this routine.

       4)  If the `eptype' input string pointer is null, the error
           SPICE(NULLPOINTER) is signaled.

       5)  If the `eptype' input string has zero length, the error
           SPICE(EMPTYSTRING) is signaled.
#### Files
       None.
#### Particulars
       The value of Delta ET is given by

          delta = ( ET - TAI ) + leap seconds

       where TAI is the atomic time corresponding to the input epoch.
#### Examples
       The following example shows how deltet_c may be used to convert
       from UTC seconds past J2000 to TDB seconds past J2000.

          deltet_c ( utcsec, "UTC", &delta );
          et = utcsec + delta

       The following example shows how deltet_c may be used to convert
       from ephemeris seconds past J2000 to UTC seconds past J2000.

          deltet_c ( et, "et", &delta );
          utcsec = et - delta;

       See the TIME Required Reading for further examples.
#### Restrictions
       1)  The routines str2et_c and et2utc_c are preferred for conversions
           between UTC and ET. This routine is provided mainly as a
           utility for str2et_c and et2utc_c.

       2)  A leapseconds kernel containing leapseconds and relativistic
           terms MUST be loaded prior to calling this function.
           Examples demonstrating how to load a kernel pool are included
           in the Required Reading file time.req and in the -Examples
           section of this header. For more general information about
           kernel pools, please consult the Required Reading file
           kernel.req.
#### Literature_References
       [1]  "The Astronomical Almanac for the Year 1990," United States
            Naval Observatory, U.S. Government Printing Office,
            Washington, D.C., 1989.
#### Author_and_Institution
       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       W.M. Owen           (JPL)
       I.M. Underwood      (JPL)
#### Version
       -CSPICE Version 1.0.1, 24-AUG-2021 (JDR)

           Edited the header to comply with NAIF standard. Added entry #2
           to -Restrictions section.

       -CSPICE Version 1.0.0, 01-AUG-2003 (NJB) (WMO) (IMU)
#### Index_Entries
       difference between ephemeris time and utc
#### Link to routine deltet_c source file deltet_c.c

    Fri Dec 31 18:41:04 2021