SIDEREALLY

Etymology

Adverb

sidereally (not comparable)

In a sidereal manner.

Source: Wiktionary

SIDEREAL

Si*de"re*al, a. Etym: [L. sidereus, from sidus, sideris, a constellation, a star. Cf. Sideral, Consider, Desire.]

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

2. (Astron.)

Definition: 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.

Source: Webster’s Unabridged Dictionary 1913 Edition