## Compute Local Apparent Sidereal Time

**Sidereal time** is the hour angle of the vernal equinox, the
ascending node of the ecliptic on the celestial equator. The daily
motion of this point provides a measure of the rotation of the Earth
with respect to the stars, rather than the Sun. Local mean sidereal
time is computed from the current Greenwich Mean Sideral Time plus
an input offset in longitude (converted to a sidereal offset by the
ratio 1.00273790935 of the mean solar day to the mean sidereal day.)
Applying the equation of equinoxes, or nutation of the mean pole of
the Earth from mean to true position, yields **local apparent
sidereal time**. Astronomers use local sidereal time because it
corresponds to the coordinate right ascension of a celestial body
that is presently on the local meridian.

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Enter Longitude :

If you don't know your longitude, use our (lower precision) value:

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