Sidereal Time Calculator
Date & TimeCalculates Greenwich Mean Sidereal Time (GMST) and Local Mean Sidereal Time (LMST) -- time measured by rotation relative to the stars, not the Sun -- for a given UT date, time, and longitude.
Greenwich Mean Sidereal Time
Sidereal time at the Greenwich meridian (0 degrees longitude).
Local Mean Sidereal Time
18h 41m 50.5s
Sidereal time adjusted for the observer longitude.
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Odeh Ahwal0people find this calculator helpful
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Date & Time calculators
Frequently Asked Questions
What is sidereal time?
Sidereal time tracks planetary rotation relative to the distant stars rather than the Sun. A sidereal day (about 23 hours, 56 minutes) is slightly shorter than a 24-hour solar day, because Earth also moves along its orbit each day, requiring a little extra rotation to bring the Sun back to the same position in the sky.
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