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Systems of Coordinates

Celestial navigation 

1stEquatorial System of Coordinates

Local Hour Angle (L.H.A)

Is the arc on the equinoctial or the angle at the pole, from the upper observer’s meridian, to the meridian of the heavenly body, measuredwestward, from 0˚ to 360˚.

Declination  (Dec.)

Is the arc on the meridian of the heavenly body, from the equinoctial, to the heavenly body, measurednorth or south, from  0 to 90˚.

 Polar Distance (P. D)

Is the arc on the meridian of the heavenly body, from the elevated pole, to the heavenly body, measured  0˚ to 180˚.

 Component of 1st equatorial system of coordinates 

                      L.H.A and Dec. / P.D

the relation  between  Dec.  And  P.D

  P.D  =  90  –  Dec         if    Lat & Dec     Same name
  P.D  =  90  +  Dec        if    Lat & Dec     Contrary name

Parallel of Declination (Diurnal Circle)

It is the apparent daily motion of the heavenly body in the westward direction.

2nd  Equatorial System of Coordinates

Sidereal Hour Angle (S.H.A)

Is the arc on the equinoctial or the angle at the pole, from the meridian      of  1stpoint of Aries, to the meridian of the heavenly body, measured westward, from 0 to 360˚.

Right Ascension (R.A)

Is the arc on the equinoctial or the angle at the pole, from the meridian of first point of Aries , to the meridian  of heavenly body, measured Eastward from 0 to 24 hours.

Greenwich Hour Angle (G.H.A)

Is the arc on the equinoctial or the angle at the pole, fromthe upper meridian of Greenwich, tothe meridian of the heavenly body, measured westward, from0˚to 360˚.