(astrology) A form of astrology that measures the position of the sun relative to the stars. This compensates for the precession of Earth's axis, which causes the zodiac signs to move around the sky relative to the vernal equinox.

(astronomy) One day of sidereal time; the time in which Earth rotates once around its axis, relative to the point of the vernal equinox (about 23 hours, 56 minutes, 4 seconds).

(astronomy) sidereal orbital period / (astronomy) sidereal rotation period

The orbital period of the Earth; a measure of the time it takes for the Sun to return to the same position with respect to the stars of the celestial sphere. A sidereal year is about 20.4 minutes longer than the tropical year (which is what is kept stable by the Gregorian calendar) due to precession of the equinoxes.

(astronomy) Time measured by the apparent diurnal motion of the vernal equinox; approximated by that based on the rotation of planet Earth relative to the seemingly fixed stars.

plural of sidereal period

plural of sidereal day

(astronomy) The sidereal year of a planet. (I.e., in the definition for "sidereal year", replace "Earth" by the given planet.)

(astronomy) The sidereal day of a planet. (I.e., in the definition for "sidereal day", replace "Earth" by the given planet.)

plural of sidereal rotation period