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Although ERA is intended to replace sidereal time, there is a need to maintain definitions for sidereal time during the transition, and when working with older data and documents. Similarly to mean solar time, every location on Earth has its own local sidereal time (LST), depending on the longitude of the point.
Sidereal time is the hour angle of the equinox. However, there are two types: if the mean equinox is used (that which only includes precession), it is called mean sidereal time; if the true equinox is used (the actual location of the equinox at a given instant), it is called apparent sidereal time.
An object's right ascension and the local sidereal time can be used to determine the time of its culmination (see hour angle). The term meridian comes from the Latin meridies , which means both "midday" and "south", as the celestial equator appears to tilt southward from the Northern Hemisphere .
A sidereal rotation is the time it takes the Earth to make one revolution with rotation to the stars, approximately 23 hours 56 minutes 4 seconds. A mean solar day is about 3 minutes 56 seconds longer than a mean sidereal day, or 1 ⁄ 366 more than a mean sidereal day. In astronomy, sidereal time is used to predict when a star will reach its ...
Rotation period with respect to distant stars, the sidereal rotation period (compared to Earth's mean Solar days) Synodic rotation period (mean Solar day) Apparent rotational period viewed from Earth Sun [i] 25.379995 days (Carrington rotation) 35 days (high latitude) 25 d 9 h 7 m 11.6 s 35 d ~28 days (equatorial) [2] Mercury: 58.6462 days [3 ...
An Egyptian method of determining the time during the night, used from at least 600 BC, was a type of plumb-line called a merkhet. A north–south meridian was created using two merkhets aligned with Polaris, the north pole star. The time was determined by observing particular stars as they crossed the meridian. [24]
Universal time tracks the Earth's rotation in time, which performs one revolution in about 24 hours. The Earth's rotation is uneven, so UT is not linear with respect to atomic time. It is practically proportional to the sidereal time, which is also a direct measure of Earth rotation. The excess revolution time is called length of day (LOD).
Sidereal, meaning "of the stars", may refer to: Sidereal time; Sidereal day; Sidereal month; Sidereal year; Sidereal period of an object orbiting another astronomical object; Sidereal and tropical astrology