NAME

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

SYNOPSIS

        use DateTime;
        use DateTime::Astro::Sunrise;

        my $dt = DateTime->new( year   => 2000,
                                month  => 6,
                                day    => 20,
                         );

       my $sunrise = DateTime::Astro::Sunrise ->new('-118','33',undef,1);

       my ($tmp_rise, $tmp_set) = $sunrise->sunrise($dt);

DESCRIPTION

       This module will return a DateTime Object for sunrise and sunset for a given day.

USAGE

       my $sunrise = DateTime::Astro::Sunrise -new(longitutide,latatude,ALT,Iteration);>
            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 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)

               Notes on Iteration
                       The orginal 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.

($sunrise, $sunset) = $sunrise->($dt);

       Returns two DateTime objects sunrise and sunset.  Please note that the time zone for these
       objects is set to UTC. So don't forget to set your timezone!!

AUTHOR

       Ron Hill rkhill@firstlight.net

CREDITS

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

       Rich Bowen (rbowen@rbowen.com)
           for suggestions

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).