sidereal.py: Internal maintenance specification

In Duffett-Smith, this is section 25.

Here are the equations defining the transformation:

For the definitions of the symbols, see Section 15.2, “AltAz.raDec(): Horizon to equatorial coordinates”.

# - - -   R A D e c . a l t A z

    def altAz ( self, h, lat ):
        """Convert equatorial to horizon coordinates.

          [ (h is an object's hour angle in radians) and
            (lat is the observer's latitude in radians) ->
              return self's position in the observer's sky
              in horizon coordinates as an AltAz instance ]
        """

As in Section 15.2, “AltAz.raDec(): Horizon to equatorial coordinates”, we will delegate most of the work to Section 16, “coordRotate(): Rotation of spherical coordinates”.

        #-- 1 --
        # [ alt  :=  altitude of self as seen from latLon at utc
        #   az  :=  azimuth of self as seen from latLon at utc ]
        alt, az  =  coordRotate ( self.dec, lat, h )

        #-- 2 --
        return AltAz ( alt, az )