For the stars, the Sidereal Hour Angle , (S.H.A.) for each star is given, and the G.H.A. of the star is obtained from the Greenwich Hour Angle of Aries as follows:
( G.H.A. Star ) = ( G.H.A. Aries ) + ( S.H.A. Star )The S.H.A. and Dec. of the stars change slowly and may be regarded as constant over periods of several days. The G.H.A. of Aries, or the Greenwich Hour Angle of the first point of Aries (the Vernal Equinox), is tabulated for each hour of the year.
The Local Hour Angle (L.H.A.) of the observer is identical to the difference in longitude ( DLO or t ) and can be obtained from the longitude of the observer by means of the formula:
t = L.H.A. =( GHA of sidereal object) - (West longitude of observer) or t = L.H.A. =( GHA of sidereal object) + (East longitude of observer)Permanent tables give the appropriate increments and corrections to the tabulated hourly values of G.H.A. and Dec. for the minutes and seconds of G.M.T.
Correction for dip = ( in minutes of angle ) (-1'.76) times the square root of (height of eye in meters) or Correction for dip = ( in minutes of angle ) (-0'.97) times the square root of (height of eye in feet)
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