DateTime::Astro::Sunrise 0.01_01

DateTime::Astro::Sunrise is a 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);

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);>
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 Suns disk touches a mathematical horizon

-0.25 degrees

Suns upper limb touches a mathematical horizon

-0.583 degrees

Center of Suns disk touches the horizon; atmospheric refraction accounted for

-0.833 degrees

Suns 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 Suns 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 Suns 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 dont forget to set your timezone!!