The function delta_et has been added to allow calculations on the position of the sun. It provides the difference between UT (approximately the same as UTC) and ET (now referred to as TDT). This function is based on a least squares fit of data from 1950 to 1991 and will need to be updated periodically. Values determined using data from 1950-1991 in the 1990 Astronomical Almanac. See DELTA_ET.WQ1 for details.