Si-dē're-al, a.
(89), a. [Lat. sideralis, and sidereus, from sidus, sideris, a constellation, a star; Fr. sidéral, sidéré, Sp. sideral, sidereo.]
- Relating to the stars; starry; astral; as, sidereal astronomy.
- (Astron.) Measured by the apparent motion of the stars; pertaining to, or 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, a clock adjusted to measure sidereal time. It usually numbers the hours from 0 to 24.—Sidereal day, the interval of time between two successive transits over the same meridian of the vernal equinox, or first point of Aries.—Sidereal time, time as reckoned by sidereal 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.—Sidereal year, the time which the sun takes in passing apparently from any fixed star around to the same star again, or one complete revolution of the earth in respect to a fixed point in space.