Sidereal

Both solar time and sidereal time make use of the regularity of Earth's rotation about its polar axis, solar time following the sun while sidereal time roughly follows the stars.

Local sidereal time at any locality differs from the Greenwich sidereal time value of the same moment, by an amount that is proportional to the longitude of the locality.

Mercury's sidereal day is about two-thirds of its orbital period, so by the prograde formula its solar day lasts for two revolutions around the sun— three times as long as its sidereal day.

When one moves eastward 15° in longitude, sidereal time is larger by one sidereal hour (note that it wraps around at 24 hours).

And Sideræl — pronounced 'sigh-deer-ee-el' — is 'a more elven' spelling of sidereal, 'the true time of the universe, star time, deep space time, not our relative earth time,' she explained.

A mean solar day is, therefore, nearly 4 minutes longer than a sidereal day.

An anomalistic month is longer than a sidereal month because the perigee moves in the same direction as the Moon is orbiting the Earth, one revolution in nine years.

A semi-synchronous orbit has an orbital period of ½ sidereal day, i.e., 11 h 58 min.

A sidereal day (the period of rotation) lasts about 58.7 Earth days.

A sidereal rotation is the time it takes the Earth to make one revolution with respect to the stars, approximately 23 hours 56 minutes 4 seconds.

A successful candidate signal would first transit the east beam, and then the west beam and do so with a speed consistent with Earth 's sidereal rotation rate.

A synodic month is longer than a sidereal month because the Earth-Moon system is orbiting the Sun in the same direction as the Moon is orbiting the Earth.

Because its rotation is so slow, Venus is very close to spherical. citation A Venusian sidereal day thus lasts longer than a Venusian year (243 versus 224.7 Earth days).

Due to the orbit of the earth around the sun a sidereal day is about 4 minutes (1/366th) less than a solar day.

Earth makes one rotation around its axis in a sidereal day; during that time it moves a short distance (about 1°) along its orbit around the sun.

Earth's sidereal day also differs from its rotation period relative to the background stars by the amount of precession in right ascension during one day (8.4 ms).

Glossary, s.v. hour angle, hour circle, sidereal time.

He also compared the lengths of the tropical year (the time it takes the Sun to return to an equinox) and the sidereal year (the time it takes the Sun to return to a fixed star), and found a slight discrepancy.

However, due to variations in the rotation rate of Earth, the rate of an ideal sidereal clock deviates from any simple multiple of a civil clock.

It is currently less than the sidereal year and its duration is very close to the mean Julian year of 365.25 days.