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

     $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

    inter is set to either 0 or 1. If set to 0 no Iteration will occur. If
    set to 1 Iteration will occur. Default is 0.

    There are a number of sun altitudes 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.

        Notes on Iteration
            ($sunrise, $sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time
            Zone,DST,ALT,inter);
                The original method only gives an approximate value of the
                Sun's rise/set times. The error rarely exceeds one or two
                minutes, but at high latitudes, when the Midnight Sun soon
                will start or just has ended, the errors may be much larger.
                If you want higher accuracy, you must then use the iteration
                feature. This feature is new as of version 0.7. Here is what
                I have tried to accomplish with this.

                a) Compute sunrise or sunset as always, with one exception:
                to convert LHA from degrees to hours, divide by 15.04107
                instead of 15.0 (this accounts for the difference between
                the solar day and the sidereal day.

                b) Re-do the computation but compute the Sun's RA and Decl,
                and also GMST0, for the moment of sunrise or sunset last
                computed.

                c) Iterate b) until the computed sunrise or sunset no longer
                changes significantly. Usually 2 iterations are enough, in
                rare cases 3 or 4 iterations may be needed.

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

            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.

	    Joshua Hoblitt [jhoblitt@ifa.hawaii.edu]
            For providing the patch to convert to DateTime


CREDITS
        Paul Schlyter, 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 Schlyter:

        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).

