Give Right Ascention of Star
Hour Min Sec
Give Greenwich Mean Time (UT)
Julian Day is the number of days elapsed since noon GMT on
January 1st, 4713 B.C.
For astronomers a day begins at noon GMT and runs until to the
Here I mean UT0 at midnight.
In Julian Date at UT are also hours, minutes and seconds in
GMST is same as GHA of Aries (Vernal Equinox).
GMST is calculated from UT.
LST is same as LHA of Aries (Vernal Equinox).
LST = GMST + Longitude
LHA = GMST + Longitude - RA
LST = LHA + RA
SHA in degrees = 360 - RA in degrees
SHA in hours = 24 - RA in hours
GHA = GMST - RA
GHA = GMST + SHA
GHA = LHA - Longitude
Astronomers uses Right Ascention (RA)
RA is measured eastward from the hour circle of Aries and
expressed in units of time.
Nautical Almanacs use Sidereal Hour Angles (SHA).
SHA is measured estward from the hour circle of Aries and
expressed in units of arc.
RA and SHA are equivalent.
Click on Button:
Julian Day at UT0: Julian Date
Greenwich Mean Sidereal Time (GMST):
Local Sidereal Time (LST): hours min sec
Local Hour Angle (LHA) of hours min sec = deg min sec
Greenwich Hour Angle (GHA) of hours min sec = deg min sec
Sidereal Hour Angle (SHA) of hours min sec = deg min sec