• Sidereal Time in Greenwich

    We will denote by Q₀ the Sidereal time in Greenwich at 0h of UT of a certain date and by Q₀ the Sidereal Time in Greenwich for any instance of the UT. To obtain the Sidereal Time at the meridian of Greenwich at 0h of UT for a certain date we must follow the next procedure:

    Calculate the julian day corresponding to the date in question at the 0h. After the calculation you should obtain a number with the termination .5. Then we calculate T by the following formula:

T = (JD - 2451545.0)/36525

    The Mean Sidereal Time in Greenwich at 0h UT it's then given by the following expression (adopted by the International Astronomical Union in 1982):

Q₀ = 6^h41^m50^s.54841 + 8640184^s.812866T + 0^s.093104T² - 0^s.0000062T³

    Note: This formula only it's intended to use only with values of T corresponding to the 0h UT in a certain date, if other values of T were used it will generated incorrect results. To obtain the Sidereal Time Q₀ in Greenwich for any instance of UT of a certain date you should multiply that instance by 1.00273790935 and add the result to the sidereal time at 0h UT.

    • Apparent Sidereal Time

    The Apparent Sidereal Time or Hour Angle of Greenwich of the True Vernal Equinox it's obtain increasing the Sidereal time by the correction Dycose, where Dy it's the nutation in longitude and e it's the obliquity of the ecliptic (see Apparent Place of a Star).