Local sidereal time is the right ascension on the upper celestial meridian. A sidereal day is approximately minutes; its angular rate is . Mean and apparent sidereal time must be paired with corresponding equatorial coordinate systems.
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Sidereal time is a timekeeping system that is based on the position of the stars as observed from Earth. Unlike solar time, which is based on the position of the Sun in the sky (and which defines a day as the time it takes for the Earth to complete one rotation relative to the Sun), sidereal time measures the Earth's rotation relative to distant celestial objects, primarily stars. A sidereal day is approximately 23 hours, 56 minutes, and 4 seconds long.