Local sidereal time is the most useful form of sidereal time since it gives the right ascension of a transiting celestial object at a given location. To compute the current local sidereal time LST, consult the current Astronomical Almanac. Look up the "G. Sidereal Time (Apparent)" GST at midnight (0 h) in the third column corresponding to the current date universal time. Let T be the current local 24-hour time, and add hours to convert from local time to Greenwich mean time.For U.S. Eastern time zone, this will be 4 hours for EDT and 5 hours for EST. Multiply by 1.0027379093 (the number of sidereal days in a solar day).Add the equation of equinoxes if desired (this is only a tenth of a second or so correction). Then subtract the west longitude (or add the east longitude) L of your location converted to hours (hours = degrees/360*24). Now add or subtract 24 hours as needed. Symbolically,


Since we used the "apparent sidereal time," the above number is actually the "local apparent sidereal time," sometimes written LAST.