Sidereal — Defs

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

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.(Astron.)

Phrases & compounds

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.