# sidereal day

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Related to sidereal days: sidereal time

## sidereal day:

see sidereal time**sidereal time**

(ST), time measured relative to the fixed stars; thus, the sidereal day is the period during which the earth completes one rotation on its axis so that some chosen star appears twice on the observer's celestial meridian.

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## sidereal day

The interval between two successive passages of a catalog equinox across a given meridian. It is divided into 24 sidereal hours. The sidereal day is 3 minutes 56 seconds shorter than the mean solar day.## Sidereal day

(religion, spiritualism, and occult)A sidereal day is the period of time it takes for Earth to complete one rotation on its axis with respect to a fixed point in space. Specifically, a sidereal day begins and ends when the local meridian for any given location on Earth passes through 0° Aries (the vernal point). Because of the motion of Earth around the Sun, sidereal days are slightly shorter than ordinary solar days. A sidereal day is 23 hours 56 minutes and 4.09 seconds in length; a sidereal hour is ½4 the length of a sidereal day.

## sidereal day

[sī′dir·ē·əl ′dā] (astronomy)

The time between two successive upper transits of the vernal equinox; this period measures one sidereal day.

## sidereal day

The period between two successive transits of a particular meridian on the earth by the first point of Aries or successive transits of the vernal equinox. Because the first point of Aries is not fixed in space and it precesses along the equinoctial 11.26” of ecliptic by arc each year, the sidereal day measured relative to Aries is minutely shorter than that measured relative to a fixed point in space. These two days are known as

*practical*and*theoretical sidereal days*, respectively. The time over the upper branch of any meridian is equal to 24 h of mean sidereal time or 23 h 56 min 4.09054 s of mean solar time.