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)
03h 22m 52.07s
50.716960 degrees
GAST (Greenwich Apparent Sidereal Time)
03h 22m 52.10s
50.717079 degrees
LMST (Local Mean Sidereal Time)
03h 22m 52.07s
50.716960 degrees
LAST (Local Apparent Sidereal Time)
03h 22m 52.10s
50.717079 degrees
Additional Parameters
Julian Date
2461072.277002
UT (hours)
18.6481
Equation of Equinoxes
0.4305s
Nutation in Longitude
7.04"
True Obliquity
23.4383 deg
Julian Century (T)
0.260842628
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).