DateTime::Astro::Sunrise - Perl DateTime extension for computing the sunrise/sunset on a given day
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.
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.
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!!
Ron Hill email@example.com
for his excellent web page on the subject.
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.