utils/SSEphem/astrtime.cc
void utc2ut1 (long mjd, double utc, long &ut1_mjd, double &ut1)
{
    ut1_mjd = mjd;
    ut1 = utc + get_ut1_offset(mjd, utc) / 86400.0;
    if (ut1 > 1.0) {
        ut1 -= 1.0;
        ut1_mjd++;
    }
    if (ut1 < 0.0) {
        ut1 += 1.0;
        ut1_mjd--;
    }
}
// Universal Time (UT1) is directly proportional to the actual rotation of
// the earth, independent of observing location.  It is the observed
// rotation of the earth (UT0) corrected for the observer's shift in
// longitude due to polar motion.  A day in UT1 is very close to a mean
// solar day.  Since the earth's rotation is not uniform, the rate of UT1 is
// not constant, and its offset from atomic time is continually changing in
// an, as yet, unpredictable way.  As of December 1995, UT1 is drifting
// about 0.8 seconds per year with respect to atomic time (TAI or UTC).
// Since UTC is intentionally incremented by integer seconds (leap seconds)
// to stay within 0.7 seconds of UT1, the difference between UT1 and UTC is
// never greater than this.  The difference, DUT1 = UT1 - UTC is monitored
// by the International Earth Rotation Service and published weekly along
// with predictions for a number of months into the future.  For the purpose
// of this routine the pblished and predicted values are kept in the ascii
// file 'iers.tab'.  UT1 is linked directly to the mean siderial time (GMST)
// through and equation as given in the Astronomical Almanac.  UT1 and,
// hence, GMST are obtained with earth rotation measures using VLBI and
// about 23 extragalactic radio sources as primary position standards.  The
// results are published as DUT1 = UT1-UTC and coordinates to the earths
// rotational pole with respect to its nominal position as defined by the
// IERS coordinate frame.
//               UT1 = UTC + DUT1 (from the 'iers.tab' file)
// The input parameters are mjd and utc (in fraction of a day), and the
// output arguments are ut1_mjd and ut1 (in fraction of a day).
Universal Time (UT1) is directly proportional to the actual rotation of
the earth, independent of observing location.  It is the observed
rotation of the earth (UT0) corrected for the observer's shift in
longitude due to polar motion.  A day in UT1 is very close to a mean
solar day.  Since the earth's rotation is not uniform, the rate of UT1 is
not constant, and its offset from atomic time is continually changing in
an, as yet, unpredictable way.  As of December 1995, UT1 is drifting
about 0.8 seconds per year with respect to atomic time (TAI or UTC).
Since UTC is intentionally incremented by integer seconds (leap seconds)
to stay within 0.7 seconds of UT1, the difference between UT1 and UTC is
never greater than this.  The difference, DUT1 = UT1 - UTC is monitored
by the International Earth Rotation Service and published weekly along
with predictions for a number of months into the future.  For the purpose
of this routine the pblished and predicted values are kept in the ascii
file 'iers.tab'.  UT1 is linked directly to the mean siderial time (GMST)
through and equation as given in the Astronomical Almanac.  UT1 and,
hence, GMST are obtained with earth rotation measures using VLBI and
about 23 extragalactic radio sources as primary position standards.  The
results are published as DUT1 = UT1-UTC and coordinates to the earths
rotational pole with respect to its nominal position as defined by the
IERS coordinate frame.
UT1 = UTC + DUT1 (from the 'iers.tab' file)
The input parameters are mjd and utc (in fraction of a day), and the
output arguments are ut1_mjd and ut1 (in fraction of a day).
Universal Time ( UT1 ) is directly proportional to the actual rotation of the earth independent of observing location . It is the observed rotation of the earth ( UT0 ) corrected for the observer ' s shift in longitude due to polar motion . A day in UT1 is very close to a mean solar day . Since the earth ' s rotation is not uniform the rate of UT1 is not constant and its offset from atomic time is continually changing in an as yet unpredictable way . As of December 1995 UT1 is drifting about 0 . 8 seconds per year with respect to atomic time ( TAI or UTC ) . Since UTC is intentionally incremented by integer seconds ( leap seconds ) to stay within 0 . 7 seconds of UT1 the difference between UT1 and UTC is never greater than this . The difference DUT1 = UT1 - UTC is monitored by the International Earth Rotation Service and published weekly along with predictions for a number of months into the future . For the purpose of this routine the pblished and predicted values are kept in the ascii file ' iers . tab ' . UT1 is linked directly to the mean siderial time ( GMST ) through and equation as given in the Astronomical Almanac . UT1 and hence GMST are obtained with earth rotation measures using VLBI and about 23 extragalactic radio sources as primary position standards . The results are published as DUT1 = UT1 - UTC and coordinates to the earths rotational pole with respect to its nominal position as defined by the IERS coordinate frame . UT1 = UTC + DUT1 ( from the ' iers . tab ' file ) The input parameters are mjd and utc ( in fraction of a day ) and the output arguments are ut1_mjd and ut1 ( in fraction of a day ) .
void utc2ut1 (long mjd, double utc, long &ut1_mjd, double &ut1)
{
    ut1_mjd = mjd;
    ut1 = utc + get_ut1_offset(mjd, utc) / 86400.0;
    if (ut1 > 1.0) {
        ut1 -= 1.0;
        ut1_mjd++;
    }
    if (ut1 < 0.0) {
        ut1 += 1.0;
        ut1_mjd--;
    }
}
void utc2ut1 ( long mjd , double utc , long & ut1_mjd , double & ut1 ) { ut1_mjd = mjd ; ut1 = utc + get_ut1_offset ( mjd , utc ) / 86400.0 ; if ( ut1 > 1.0 ) { ut1 -= 1.0 ; ut1_mjd ++ ; } if ( ut1 < 0.0 ) { ut1 += 1.0 ; ut1_mjd -- ; } }
Universal Time (UT1) is directly proportional to the actual rotation of
the earth, independent of observing location.
Universal Time ( UT1 ) is directly proportional to the actual rotation of the earth independent of observing location .