Greenwich Mean Sidereal Time

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Greenwich Mean Sidereal Time (Longitude 0°) at 0h UTC and at 18h UTC:

UTC - Date	GMST at 00h UTC	GMST at 18h UTC
2018 - 02 - 01	08 h 44 m 37.0 s	02 h 47 m 34.5 s
2018 - 02 - 02	08 h 48 m 33.6 s	02 h 51 m 31.0 s
2018 - 02 - 03	08 h 52 m 30.1 s	02 h 55 m 27.6 s
2018 - 02 - 04	08 h 56 m 26.7 s	02 h 59 m 24.1 s
2018 - 02 - 05	09 h 00 m 23.3 s	03 h 03 m 20.7 s
2018 - 02 - 06	09 h 04 m 19.8 s	03 h 07 m 17.2 s
2018 - 02 - 07	09 h 08 m 16.4 s	03 h 11 m 13.8 s
2018 - 02 - 08	09 h 12 m 12.9 s	03 h 15 m 10.3 s
2018 - 02 - 09	09 h 16 m 09.5 s	03 h 19 m 06.9 s
2018 - 02 - 10	09 h 20 m 06.0 s	03 h 23 m 03.4 s
2018 - 02 - 11	09 h 24 m 02.6 s	03 h 27 m 00.0 s
2018 - 02 - 12	09 h 27 m 59.1 s	03 h 30 m 56.6 s
2018 - 02 - 13	09 h 31 m 55.7 s	03 h 34 m 53.1 s
2018 - 02 - 14	09 h 35 m 52.3 s	03 h 38 m 49.7 s
2018 - 02 - 15	09 h 39 m 48.8 s	03 h 42 m 46.2 s
2018 - 02 - 16	09 h 43 m 45.4 s	03 h 46 m 42.8 s
2018 - 02 - 17	09 h 47 m 41.9 s	03 h 50 m 39.3 s
2018 - 02 - 18	09 h 51 m 38.5 s	03 h 54 m 35.9 s
2018 - 02 - 19	09 h 55 m 35.0 s	03 h 58 m 32.4 s
2018 - 02 - 20	09 h 59 m 31.6 s	04 h 02 m 29.0 s
2018 - 02 - 21	10 h 03 m 28.1 s	04 h 06 m 25.6 s
2018 - 02 - 22	10 h 07 m 24.7 s	04 h 10 m 22.1 s
2018 - 02 - 23	10 h 11 m 21.3 s	04 h 14 m 18.7 s
2018 - 02 - 24	10 h 15 m 17.8 s	04 h 18 m 15.2 s
2018 - 02 - 25	10 h 19 m 14.4 s	04 h 22 m 11.8 s
2018 - 02 - 26	10 h 23 m 10.9 s	04 h 26 m 08.3 s
2018 - 02 - 27	10 h 27 m 07.5 s	04 h 30 m 04.9 s
2018 - 02 - 28	10 h 31 m 04.0 s	04 h 34 m 01.4 s

The sidereal time is a local time. To calculate your Local Mean Sidereal Time (LMST) add to the GMST four minutes of time for every 1 degree eastern longitude - add four seconds of time for every 1 minute of arc eastern longitude - add one second of time for every 15 seconds of arc eastern longitude. For western longitudes it is necessary to subtract.

What is Sidereal Time?

Using the sidereal time, the astronomer will be able to find the desired celestial object in the sky.
One sidereal day is the time between two upper transits across the observer's local meridian of the vernal equinox. The current sidereal time is equal to the hour angle of the vernal equinox. To calculate the hour angel of a certain celestial object subtract the object's right ascension to the sidereal time.
Because sidereal time is measured relative to the stars and not to the sun, Sidereal Clocks must gain approximately 3m 56s per day on clocks keeping mean solar time.

Software Sidereal Time Clocks:

A Sidereal Time Clock for Windows®: download aclk2.zip 90kB, free
A high-precision Astronomical Clock for MSDOS® and Windows®, free. Info and download Maxclock
A Sidereal Time Clock for Palm OS®, Info and download Palm

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