NAME
    Astro::Sunrise - Perl extension for computing the sunrise/sunset on a
    given day

SYNOPSIS
     use Astro::Sunrise;

     ($sunrise, $sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST);
     ($sunrise, $sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST,ALT);

     $sunrise = sun_rise(longitude,latitude);
     $sunset = sun_set(longitude,latitude);

     $sunrise = sun_rise(longitude,latitude,ALT);
     $sunset = sun_set(longitude,latitude,ALT);

     $sunrise = sun_rise(longitude,latitude,ALT,day_offset);
     $sunset = sun_set(longitude,latitude,ALT,day_offset);

DESCRIPTION
    This module will return the sunrise/sunset for a given day.

     Eastern longitude is entered as a positive number
     Western longitude is entered as a negative number
     Northern latitude is entered as a positive number
     Southern latitude is entered as a negative number

    There are a number of sun altitides to chose from. The default is -0.833
    because this is what most countries use. Feel free to specify it if you
    need to. Here is the list of values to specify altitude (ALT) with:

    0 degrees
        Center of Sun's disk touches a mathematical horizon

    -0.25 degrees
        Sun's upper limb touches a mathematical horizon

    -0.583 degrees
        Center of Sun's disk touches the horizon; atmospheric refraction
        accounted for

    -0.833 degrees
        Sun's supper limb touches the horizon; atmospheric refraction
        accounted for

    -6 degrees
        Civil twilight (one can no longer read outside without artificial
        illumination)

    -12 degrees
        Nautical twilight (navigation using a sea horizon no longer
        possible)

    -15 degrees
        Amateur astronomical twilight (the sky is dark enough for most
        astronomical observations)

    -18 degrees
        Astronomical twilight (the sky is completely dark)

USAGE
    sunrise
        "($sunrise, $sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time
        Zone,DST);"
        "($sunrise, $sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time
        Zone,DST,ALT);"
            Returns the sunrise and sunset times, in HH:MM format. (Note:
            Time Zone is the offset from GMT and DST is daylight savings
            time, 1 means DST is in effect and 0 is not). In the first form,
            a default altitude of -.0833 is used. In the second form, the
            altitude is specified as the last argument. Note that adding 1
            to the Time Zone during DST and specifying DST as 0 is the same
            as indicating the Time Zone correctly and specifying DST as 1.

        *For Example*
             ($sunrise, $sunset) = sunrise( 2001, 3, 10, 17.384, 98.625, -5, 0 );
             ($sunrise, $sunset) = sunrise( 2002, 10, 14, -105.181, 41.324, -7, 1, -18);

    sun_rise
        "$sun_rise = sun_rise( longitude, latitude );"
        "$sun_rise = sun_rise( longitude, latitude, ALT );"
        "$sun_rise = sun_rise( longitude, latitude, ALT, day_offset );"
            Returns the sun rise time for the given location. The first form
            uses today's date (from Time::Object) and the default altitude.
            The second form adds specifying a custom altitude. The third
            form allows for specifying an integer day offset from today,
            either positive or negative.

        *For Example*
             $sunrise = sun_rise( -105.181, 41.324 );
             $sunrise = sun_rise( -105.181, 41.324, -15 );
             $sunrise = sun_rise( -105.181, 41.324, -12, +3 );
             $sunrise = sun_rise( -105.181, 41.324, undef, -12);

    sun_set
        "$sun_set = sun_set( longitude, latitude );"
        "$sun_set = sun_set( longitude, latitude, ALT );"
        "$sun_set = sun_set( longitude, latitude, ALT, day_offset );"
            Returns the sun set time for the given location. The first form
            uses today's date (from Time::Object) and the default altitude.
            The second form adds specifying a custom altitude. The third
            form allows for specifying an integer day offset from today,
            either positive or negative.

        *For Example*
             $sunrise = sun_set( -105.181, 41.324 );
             $sunrise = sun_set( -105.181, 41.324, -15 );
             $sunrise = sun_set( -105.181, 41.324, -12, +3 );
             $sunrise = sun_set( -105.181, 41.324, undef, -12);

AUTHOR
    Ron Hill rkhill@firstlight.net

SPECIAL THANKS
    Robert Creager [Astro-Sunrise@LogicalChaos.org] For providing help with
    converting Paul's C code to perl For providing code for sun_rise,
    sun_set sub's Also adding options for different altitudes

CREDITS
    Paul Schlyer, Stockholm, Sweden
    for his excellent web page on the subject.

    Rich Bowen (rbowen@rbowen.com)
    for suggestions

    Adrian Blockley [adrian.blockley@environ.wa.gov.au]
    for finding a bug in the conversion to local time

    Lightly verified against
    http://aa.usno.navy.mil/data/docs/RS_OneYear.html

COPYRIGHT and LICENSE
    Here is the copyright information provided by Paul Schlyer:

    Written as DAYLEN.C, 1989-08-16

    Modified to SUNRISET.C, 1992-12-01

    (c) Paul Schlyter, 1989, 1992

    Released to the public domain by Paul Schlyter, December 1992

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.

BUGS
SEE ALSO
    perl(1).