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Calculate sunrise and sunset times for the current or targetted day.
The times can be adjusted either for twilight or fixed durations.

The program can either: wait for sunrise or sunset   (function: wait),
  or return the time (GMT or local) the event occurs (function: list),
  or report the day length and twilight timings      (function: report),
  or simply report if it is DAY or NIGHT             (function: poll).

You should specify the latitude and longitude of your target location.


Usage: sunwait [major options] [minor options] [twilight type] [rise|set] [offset] [latitude] [longitude]

Major options, either:
    poll          Returns immediately indicating DAY or NIGHT. See 'program exit codes'. Default.
    wait          Sleep until specified event occurs. Else exit immediate.
    list [X]      Report twilight times for next 'X' days (inclusive). Default: 1.
    report [date] Generate a report about the days sunrise and sunset timings. Default: the current day

Minor options, any of:
    [no]debug     Print extra info and returns in one minute. Default: nodebug.
    [no]version   Print the version number. Default: noversion.
    [no]help      Print this help. Default: nohelp.
    [no]gmt       Print times in GMT or local-time.  Default: nogmt.

Twilight types, either:
    daylight      Top of sun just below the horizon. Default.
    civil         Civil Twilight.         -6 degrees below horizon.
    nautical      Nautical twilight.     -12 degrees below horizon.
    astronomical  Astronomical twilight. -18 degrees below horizon.
    angle [X.XX]  User-specified twilight-angle (degrees). Default: 0.

Sunrise/sunset. Only useful with major-options: 'wait' and 'list'. Any of: (default: both)
    rise          Wait for the sun to rise past specified twilight & offset.
    set           Wait for the sun to  set past specified twilight & offset.

Offset:
    offset [MM|HH:MM] Time interval (+ve towards noon) to adjust twilight calculation.

Target date. Only useful with major-options: 'report' or 'list'. Default: today
    d [DD]        Set the target Day-of-Month to calculate for. 1 to 31.
    m [MM]        Set the target Month to calculate for. 1 to 12.
    y [YYYY]      Set the target Year to calculate for. 2000 to 2099.

latitude/longitude coordinates: floating-point degrees, with [NESW] appended. Default: Bingham, England.

Exit (return) codes:
    0           OK: exit from 'wait' or 'list' only.
    1           Error.
    2           Exit from 'poll': it is DAY or twilight.
    3           Exit from 'poll': it is NIGHT (after twilight).

Example 1: sunwait wait rise offset -1:15:10 51.477932N 0.000000E
Wait until 1 hour 15 minutes 10 secs before the sun rises in Greenwich, London.

Example 2: sunwait list 7 civil 55.752163N 37.617524E
List civil sunrise and sunset times for today and next 6 days. Moscow.

Example 3: sunwait poll exit angle 10 54.897786N -1.517536E
Indicate by program exit-code if is Day or Night using a custom twilight angle of 10 degrees above horizon. Washington, UK.

Example 4: sunwait list 7 gmt sunrise angle 3
List next 7 days sunrise times, custom +3 degree twilight angle, default location.
Uses GMT; as any change in daylight saving over the specified period is not considered.

Example 5: sunwait report y 20 m 3 d 15 10.49S 105.55E
Produce a report of the different sunrises and sunsets on an arbitrary day (2022/03/15) for an arbitrary location (Christmas Island)

Note that program uses C library functions to determine time and localtime.
Error for timings are estimated at: +/- 4 minutes.