Sidereal Time Calculator

Your details

The UTC calendar year, 1900 to 2100.
UTC month, 1 = January, 12 = December.
UTC calendar day of the month.
UTC hour in 24-hour format. If you have local time, convert to UTC first by adding or subtracting your UTC offset.
Decimal degrees east of Greenwich. East longitudes are positive, west are negative. New York City is about -74.0, London is 0.0, Tokyo is about +139.7.
deg
Right ascension of a star or object in decimal degrees (0 to 360). If left blank, the hour angle is not computed. Convert h:m:s RA by multiplying hours by 15.
deg
GMST
14:01:04

Greenwich Mean Sidereal Time in hh:mm:ss

GAST14:01:04
LMST09:05:03
LAST09:05:03
Hour Angle+09:05:03
Julian Date2,460,848.33333
GMST (degrees)210.2666 deg
LMST (degrees)136.2606 deg
210.26664131181315 h
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LAST is 09:05:03 for your observer location.

  • Your Local Apparent Sidereal Time (LAST) is 09:05:03. Any star with a right ascension equal to this value is currently on your meridian.
  • LMST is 09:05:03 for longitude 74.006 W. LAST differs from LMST by the equation of the equinoxes, which is usually less than one second of time.
  • The Julian Date for this UTC instant is 2460848.33333, the continuous day count used in all astronomical calculations.
  • Hour angle for the entered RA is +09:05:03: a positive value means the object has already passed your meridian and is descending to the west.

Next stepCompare your LAST to the right ascension of your target to decide whether to observe now or wait for the object to rise above the horizon.

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