DateTime::Event::Sunrise(3pm)				User Contributed Perl Documentation			     DateTime::Event::Sunrise(3pm)

NAME

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

SYNOPSIS

	use DateTime;
	use DateTime::Event::Sunrise;

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

	my $sunrise = DateTime::Event::Sunrise ->sunrise (
			       longitude =>'-118',
			       latitude =>'33',
			       altitude => '-0.833',
			       iteration => '1'
			 );

	my $sunset = DateTime::Event::Sunrise ->sunset (
			       longitude =>'-118',
			       latitude =>'33',
			       altitude => '-0.833',
			       iteration => '1'
			 );

	my $tmp_rise = $sunrise->next( $dt );

	my $dt2 = DateTime->new( year	=> 2000,
				month  => 12,
				day    => 31,
			  );

	# iterator
	my $dt_span = DateTime::Span->new( start =>$dt1, end=>$dt2 );
	my $set = $sunrise->intersection($dt_span);
	my $iter = $set->iterator;
	while ( my $dt = $iter->next ) {
	    print ' ',$dt->datetime;
	}

	# is it day or night?
	my $day_set = DateTime::SpanSet->from_sets(
	    start_set => $sunrise, end_set => $sunset );
	print $day_set->contains( $dt ) ? 'day' : 'night';

       my $dt = DateTime->new( year   => 2000,		  month  => 6,		  day	 => 20,
			time_zone => 'America/Los_Angeles',
			 );

       my $sunrise = DateTime::Event::Sunrise ->new(
			    longitude =>'-118' ,		latitude => '33',		 altitude => '-0.833',			 iteration
       => '1'

       );

       my $tmp = $sunrise->sunrise_sunset_span($dt); print "Sunrise is:" , $tmp->start->datetime , "
"; print "Sunset is:" , $tmp->end->datetime;

       my $dt1 = $sunrise->sunrise_datetime( $dt ); print "Sunrise is:" , $dt1->datetime  , "
"; my $dt2 = $sunrise->sunset_datetime( $dt );
       print "Sunset is:" ,  $dt2->datetime , "
";

DESCRIPTION

       This module will return a DateTime recurrence set for sunrise or sunset.

METHODS

       sunrise, sunset, sunrise_sunset_span, sunrise_datetime, sunset_datetime

	my $sunrise = DateTime::Event::Sunrise ->sunrise (
			       longitude => '-118',
			       latitude =>  '33',
			       altitude =>  '-0.833',
			       iteration => '1'
			  );

	my $sunset = DateTime::Event::Sunrise ->sunset (
			       longitude => '-118',
			       latitude =>  '33',
			       altitude =>  '-0.833',
			       iteration => '1'
			  );
	my $sunrise_span = DateTime::Event::Sunrise ->new (
			       longitude => '-118',
			       latitude =>  '33',
			       altitude =>  '-0.833',
			       iteration => '1'
			  );
	my $both_times = $sunrise_span->sunrise_sunset_span($dt);
	print "Sunrise is:" , $both_times->start->datetime;
	print "Sunset is:" , $both_times->end->datetime;

	my $dt1 = $sunrise->sunrise_datetime( $dt );
	print "Sunrise is:" , $dt1->datetime  , "
";
	my $dt2 = $sunrise->sunset_datetime( $dt );
	print "Sunset is:" ,  $dt2->datetime , "
";

	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

       Iteration 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 (Altitude) 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 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.

       next current previous contains as_list iterator

       See DateTime::Set.

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

       Internal method.

       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

SPECIAL THANKS

       Robert Creager [Astro-Sunrise@LogicalChaos.org]
	   for providing help with converting Paul's C code to perl.

       Flavio S. Glock [fglock@pucrs.br]
	   for providing the the interface to the DateTime::Set module.

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 MER-
       CHANTABILITY, 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.

SEE ALSO

       perl(1).

       DateTime Web page at http://datetime.perl.org/

       DateTime::Set documentation

       DateTime::SpanSet documentation

perl v5.8.8							    2004-03-31					     DateTime::Event::Sunrise(3pm)