Return the value of Delta ET (ET-UTC) for an input epoch.
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.
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 indicates 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).
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 true.
The value of Delta ET is given by delta = ( ET - TAI ) + leap seconds where TAI is the atomic time corresponding to the input epoch.
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.
The routines str2et_c and timout_c are preferred for conversions between UTC string and ET represented as seconds past J2000 TDB. This routine is provided mainly to provide a method of representing an epoch as UTC seconds past J2000.
1) If the input epoch is not recognized, the error SPICE(INVALIDEPOCH) is signaled. 2) If the variables necessary for the computation of delta have not been loaded into the kernel pool, the error SPICE(KERNELVARNOTFOUND) is signaled. 3) If the number of leapseconds in the pool is greater than the local leapseconds buffer size, the error SPICE(BUFFEROVERFLOW) is signaled. 4) The error SPICE(EMPTYSTRING) is signaled if the input string `eptype' does not contain at least one character, since the input string cannot be converted to a Fortran-style string in this case. 5) The error SPICE(NULLPOINTER) is signaled if the input string pointer is null.
N.J. Bachman (JPL) W.M. Owen (JPL) I.M. Underwood (JPL)
 Astronomical Almanac.
-CSPICE Version 1.0.0, 01-AUG-2003 (NJB) (WMO) (IMU)
difference between ephemeris time and utc