Sidereal

Part of speech: adjective (a.)

1. Relating to the stars; starry; astral; as, sidereal astronomy.

2. Measuring by the apparent motion of the stars; designated, marked out, or accompanied, by a return to the same position in respect to the stars; as, the sidereal revolution of a planet; a sidereal day. Sidereal clock, day, month, year. See under Clock, Day, etc. -- Sideral time, time as reckoned by sideral days, or, taking the sidereal day as the unit, the time elapsed since a transit of the vernal equinox, reckoned in parts of a sidereal day. This is, strictly, apparent sidereal time, mean sidereal time being reckoned from the transit, not of the true, but of the mean, equinoctial point.