. Computer Ephemeris. Sidereal time. Explanations. Each row contains at 0h of Universal time: month, day, real sidereal time (hours, minutes, seconds), mean sidereal time (only seconds, as a rule, hours and minutes are the same as in real time) and nutation in right ascension: long periodic (with periods greater than 35 days), and then short periodic (periods less than 35 days). Standard IAU 1980 nutation theory is used.