NAME

       sundazel - Compute the time of Solar passage

SYNOPSIS

       sundazel [<option>] [<yyyymmdd>]

DESCRIPTION

       sundazel  computes  the  local  time  of  the  Sun's  passage through the specified apparent longitude or
       latitude in a user-defined coordinate system, for the specified location on the specified  date  (default
       today).

       The Sun's apparent hour angle, azimuth, elevation, and the longitude and latitude in user coordinates are
       also printed, in degrees.  Refraction is accounted for.

       sundazel  may  also  be  used  to  compute  the  time  of  sunrise and set, the Sun's right ascension and
       declination, and the Equation of Time.

OPTIONS

       -p <option>

              The Solar passage required and, if relevant, the coordinate value in degrees:

       sunrise
              Sunrise.

       sunset Sunset.

       lng=<lng>
              Longitude of the Sun in the user-defined coordinate system.

       lat=<lat>
              Latitude of the Sun in the user-defined coordinate system.

       -l <lng>,<lat>

              Longitude and latitude of the observer.

       -t <tz>

              The observer's time zone, positive east of Greenwich (hr).

       -u <az>,<el>,<zlng>

              Azimuth and elevation of the pole of the user-defined coordinate system, and the longitude of  the
              zenith (deg).  See below.

       -n     Set  the  user-defined  coordinate  system as one with pole due north on the horizon, with zero of
              longitude at the zenith.

       -w     Set the user-defined coordinate system as one with pole due west on  the  horizon,  with  zero  of
              longitude at the zenith.

       -v     Also print the Sun's right ascension, declination (deg), and the Equation of Time (min).

       The  user-defined  coordinate  system  is a right-handed spherical coordinate system with its pole at the
       specified azimuth and elevation, and with zenith having the specified longitude.  If omitted, the default
       is a right-handed system with its pole at the zenith and  prime  meridian  due  north,  i.e.  similar  to
       azimuth  and  elevation  except that longitude increases in the reverse sense to azimuth, i.e. from north
       through west rather than north through east.

       Setting a range of azimuth or elevation often provides a poor criterion for timing  the  passage  of  the
       Sun,  for  example  in  determining when it shines directly through a skylight, or when an awning casts a
       shadow on a particular point on the ground.  In such cases the projection of the skylight or awning  from
       the  ground  onto the sky should be considered.  Some other coordinate system may provide a better fit to
       the region of the sky thereby defined.  For example, the passage of the Sun across a skylight oriented at
       azimuth alpha might be handled via a coordinate system with pole on  the  horizon  at  that  azimuth  and
       considering  the  Sun's  passage through a range of longitude in this system.  Perhaps better might be to
       use a coordinate system with pole at alpha-90 and considering a range of latitude.

       Sunrise and sunset correspond to first/last contact of the Sun's limb on the  horizon,  corresponding  to
       apparent  elevation -0.27 deg (true elevation -0.79 deg).  If no options are specified, the default is to
       calculate the time of sunset.  If more than one p option is specified, only the last is effective.

sundazel 8.2.2                                    November 2023                                      SUNDAZEL(1)