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.