1SUNDAZEL(1)                      User Commands                     SUNDAZEL(1)
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NAME

6       sundazel - Compute the time of Solar passage
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SYNOPSIS

9       sundazel [<option>] [<yyyymmdd>]
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DESCRIPTION

12       sundazel computes the local time of the Sun's passage through the spec‐
13       ified apparent longitude or latitude in a user-defined coordinate  sys‐
14       tem, for the specified location on the specified date (default today).
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16       The  Sun's  apparent  hour angle, azimuth, elevation, and the longitude
17       and latitude in user coordinates are also printed, in degrees.  Refrac‐
18       tion is accounted for.
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20       sundazel  may  also be used to compute the time of sunrise and set, the
21       Sun's right ascension and declination, and the Equation of Time.
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OPTIONS

24       -p <option>
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26              The Solar passage required  and,  if  relevant,  the  coordinate
27              value in degrees:
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29       sunrise
30              Sunrise.
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32       sunset Sunset.
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34       lng=<lng>
35              Longitude of the Sun in the user-defined coordinate system.
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37       lat=<lat>
38              Latitude of the Sun in the user-defined coordinate system.
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40       -l <lng>,<lat>
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42              Longitude and latitude of the observer.
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44       -t <tz>
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46              The observer's time zone, positive east of Greenwich (hr).
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48       -u <az>,<el>,<zlng>
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50              Azimuth and elevation of the pole of the user-defined coordinate
51              system, and the longitude of the zenith (deg).  See below.
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53       -n     Set the user-defined coordinate system  as  one  with  pole  due
54              north on the horizon, with zero of longitude at the zenith.
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56       -w     Set the user-defined coordinate system as one with pole due west
57              on the horizon, with zero of longitude at the zenith.
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59       -v     Also print the Sun's right ascension, declination (deg), and the
60              Equation of Time (min).
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62       The  user-defined coordinate system is a right-handed spherical coordi‐
63       nate system with its pole at the specified azimuth and  elevation,  and
64       with zenith having the specified longitude.  If omitted, the default is
65       a right-handed system with its pole at the zenith  and  prime  meridian
66       due  north, i.e. similar to azimuth and elevation except that longitude
67       increases in the reverse sense to azimuth, i.e. from north through west
68       rather than north through east.
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70       Setting a range of azimuth or elevation often provides a poor criterion
71       for timing the passage of the Sun, for example in determining  when  it
72       shines directly through a skylight, or when an awning casts a shadow on
73       a particular point on the ground.  In such cases the projection of  the
74       skylight  or  awning from the ground onto the sky should be considered.
75       Some other coordinate system may provide a better fit to the region  of
76       the  sky thereby defined.  For example, the passage of the Sun across a
77       skylight oriented at azimuth alpha might be handled  via  a  coordinate
78       system  with  pole  on  the horizon at that azimuth and considering the
79       Sun's passage through a range of longitude  in  this  system.   Perhaps
80       better  might  be  to use a coordinate system with pole at alpha-90 and
81       considering a range of latitude.
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83       Sunrise and sunset correspond to first/last contact of the  Sun's  limb
84       on the horizon, corresponding to apparent elevation -0.27 deg (true el‐
85       evation -0.79 deg).  If no options are specified,  the  default  is  to
86       calculate  the time of sunset.  If more than one p option is specified,
87       only the last is effective.
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91sundazel 7.6                      April 2021                       SUNDAZEL(1)
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