FRAME

        [ASTRO\]FRAME System [...]

    This command specifies the reference frame to be used for plots.  System
    may be HORIZONTAL or EQUATORIAL (at epoch defined by TIME command) If no
    other  argument  is  given,  plotting is done in rectangular coordinates
    representing Azimuth-Elevation or Right Ascension-Declination.  If other
    arguments are given, a Stereographic projection is used:
      - FRAME EQUATORIAL Ra Dec Size
        the  projection  will  be  centered on Ra and Dec (hours - degrees);
        Size in degrees specify the plotting range (e.g.  180  for  a  whole
        hemisphere = the default).
      - FRAME HORIZONTAL Az El Size
        same thing, but Az and El are in degrees.
      - FRAME HORIZONTAL Center
        will  plot  a  hemisphere  in horizontal system, where Center may be
        ZENITH, NORTH, EAST, SOUTH or WEST.