Sidereal Time Calculator

Sidereal Time Calculator

Date

Local Time (24h)

Longitude (degrees, East positive)

Please enter a valid longitude (-180 to 180).

Timezone offset from UTC (hours)

Please enter a valid timezone offset (-12 to 14).

Results

Greenwich Sidereal Time (GST): hours

Local Sidereal Time (LST): hours

Formula: First, compute Julian Date (JD) from the given date and time. Then, GST = 280.46061837 + 360.98564736629 * (JD - 2451545.0) + 0.000387933 * T^2 - T^3/38710000, where T is centuries since J2000. Adjust to [0,24) hours. LST = (GST + longitude/15) mod 24.