Sidereal time now
Sidereal time tracks the Earth's turn relative to the stars rather than the Sun. Astronomers use local sidereal time to know which part of the sky is overhead.
Local sidereal time ()
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Greenwich apparent sidereal time
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What is sidereal time?
A sidereal day, one turn of the Earth relative to the distant stars, is about 23 hours 56 minutes 4 seconds, nearly four minutes shorter than a solar day. So sidereal time gains about four minutes on clock time every day and goes all the way round the clock in a year.
Local sidereal time equals the right ascension of the stars crossing your meridian (due south in the northern hemisphere) right now. If your LST is 05:35, the Orion Nebula (right ascension about 5h 35m) is at its highest. Calculated with the open-source Astronomy Engine. See also planets tonight and the moon phase.
More converters: minutes to decimal · decimal hours to time · seconds converter · hours to minutes · day of the year · ISO 8601 · Unix timestamp · Julian date · sidereal time
Questions people ask
What is local sidereal time?
The sidereal time at your longitude: Greenwich sidereal time plus your longitude in hours (east positive). It tells you which right ascension is on your meridian.
How long is a sidereal day?
23 hours, 56 minutes and about 4.09 seconds.
Why is sidereal time different from solar time?
Because the Earth also moves along its orbit, it has to turn a little extra each day to bring the Sun back to the same place, about four minutes more than one turn relative to the stars.