Sidereal Time Calculator
Calculate Greenwich Mean Sidereal Time (GMST), Greenwich Apparent Sidereal Time (GAST), and Local Sidereal Time (LST). Sidereal time is essential for astronomical observations.
Sidereal Time Results
GMST (Greenwich Mean Sidereal Time)
22h 38m 23.78s
339.599083 degrees
GAST (Greenwich Apparent Sidereal Time)
22h 38m 23.80s
339.599186 degrees
LMST (Local Mean Sidereal Time)
22h 38m 23.78s
339.599083 degrees
LAST (Local Apparent Sidereal Time)
22h 38m 23.80s
339.599186 degrees
Additional Parameters
Julian Date
2461178.787836
UT (hours)
6.9081
Equation of Equinoxes
0.3715s
Nutation in Longitude
6.07"
True Obliquity
23.4381 deg
Julian Century (T)
0.263758736
About Sidereal Time
Sidereal time is the hour angle of the vernal equinox. A sidereal day is about 23 hours, 56 minutes, 4 seconds - shorter than a solar day because Earth moves in its orbit. Mean sidereal time uses a fictitious mean equinox, while apparent sidereal time accounts for nutation. Local sidereal time equals GMST plus the observer's longitude (in hours).
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