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

Provided by: libdatetime-event-sunrise-perl_0.0505-2_all

NAME

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

SYNOPSIS

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

         # generating DateTime objects from a DateTime::Event::Sunrise object
         my $sun_Kyiv = DateTime::Event::Sunrise->new(longitude => +30.85,  # 30°51'E
                                                      latitude  => +50.45); # 50°27'N
         for (12, 13, 14) {
           my $dt_yapc_eu = DateTime->new(year      => 2013,
                                          month     =>    8,
                                          day       =>   $_,
                                          time_zone => 'Europe/Kiev');
           say "In Kyiv (50°27'N, 30°51'E) on ", $dt_yapc_eu->ymd, " sunrise occurs at ", $sun_Kyiv->sunrise_datetime($dt_yapc_eu)->hms,
                                                                " and sunset occurs at ", $sun_Kyiv->sunset_datetime ($dt_yapc_eu)->hms;
         }

         # generating DateTime objects from DateTime::Set objects
         my $sunrise_Austin = DateTime::Event::Sunrise->sunrise(longitude => -94.73,  # 97°44'W
                                                                latitude  => +30.3);  # 30°18'N
         my $sunset_Austin  = DateTime::Event::Sunrise->sunset (longitude => -94.73,
                                                                latitude  => +30.3);
         my $dt_yapc_na_rise = DateTime->new(year      => 2013,
                                             month     =>    6,
                                             day       =>    3,
                                             time_zone => 'America/Chicago');
         my $dt_yapc_na_set = $dt_yapc_na_rise->clone;
         say "In Austin (30°18'N, 97°44'W), sunrises and sunsets are";
         for (1..3) {
           $dt_yapc_na_rise = $sunrise_Austin->next($dt_yapc_na_rise);
           $dt_yapc_na_set  = $sunset_Austin ->next($dt_yapc_na_set);
           say $dt_yapc_na_rise, ' ', $dt_yapc_na_set;
         }

         # If you deal with a polar location
         my $sun_in_Halley = DateTime::Event::Sunrise->new(
                                        longitude => -26.65, # 26°39'W
                                        latitude  => -75.58, # 75°35'S
                                        precise   => 1,
                                        );
         my $Alex_arrival = DateTime->new(year  => 2006, # approximate date, not necessarily the exact one
                                          month =>    1,
                                          day   =>   15,
                                          time_zone => 'Antarctica/Rothera');
         say $Alex_arrival->strftime("Alex Gough (a Perl programmer) arrived at Halley Base on %Y-%m-%d.");
         if ($sun_in_Halley->is_polar_day($Alex_arrival)) {
           say "It would be days, maybe weeks, before the sun would set.";
         }
         elsif ($sun_in_Halley->is_polar_night($Alex_arrival)) {
           say "It would be days, maybe weeks, before the sun would rise.";
         }
         else {
           my $sunset = $sun_in_Halley->sunset_datetime($Alex_arrival);
           say $sunset->strftime("And he saw his first antarctic sunset at %H:%M:%S.");
         }

DESCRIPTION

       This module will computes the time of sunrise and sunset for a given date and a given location. The
       computation uses Paul Schlyter's algorithm.

       Actually, the module creates a DateTime::Event::Sunrise object or a DateTime::Set object, which are used
       to generate the sunrise or the sunset times for a given location and for any date.

METHODS

new
This is the DateTime::Event::Sunrise constructor. It takes keyword parameters, which are:

longitude
This is the longitude of the location where the sunrises and sunsets are observed. It is given as
decimal degrees: no minutes, no seconds, but tenths and hundredths of degrees. Another break with
the normal usage is that Eastern longitude are positive, Western longitudes are negative.

Default value is 0, that is Greenwich or any location on the eponymous meridian.

latitude
This is the latitude of the location where the sunrises and sunsets are observed. As for the
longitude, it is given as decimal degrees. Northern latitudes are positive numbers, Southern
latitudes are negative numbers.

Default value is 0, that is any location on the equator.

altitude
This is the height of the Sun at sunrise or sunset. In astronomical context, the altitude or height
is the angle between the Sun and the local horizon. It is expressed as degrees, usually with a
negative number, since the Sun is below the horizon.

Default value is -0.833, that is when the sun's upper limb touches the horizon, while taking in
account the light refraction.

Positive altitude are allowed, in case the location is near a mountain range behind which the sun
rises or sets.

precise
Boolean to control which algorithm is used. A false value gives a simple algorithm, but which can
lead to inaccurate sunrise times and sunset times. A true value gives a more elaborate algorithm,
with a loop to refine the sunrise and sunset times and obtain a better precision.

Default value is 0, to choose the simple algorithm.

This parameter replaces the "iteration" deprecated parameter.

upper_limb
Boolean to choose between checking the Sun's upper limb or its center. A true value selects the
upper limb, a false value selects the center.

This parameter is significant only when the altitude does not already deal with the sun radius. When
the altitude takes into account the sun radius, this parameter should be false.

Default value is 0, since the upper limb correction is already taken in account with the default
-0.833 altitude.

silent
Boolean to control the output of some warning messages. With polar locations and dates near the
winter solstice or the summer solstice, it may happen that the sun never rises above the horizon or
never sets below. If this parameter is set to false, the module will send warnings for these
conditions. If this parameter is set to true, the module will not pollute your STDERR stream.

Default value is 0, for backward compatibility.

sunrise, sunset
Although they come from the DateTime::Event::Sunrise module, these methods are "DateTime::Set"
constructors. They use the same parameters as the "new" constructor, but they give objects from a
different class.

sunrise_datetime, sunset_datetime
These two methods apply to "DateTime::Event::Sunrise" objects (that is, created with "new", not "sunrise"
or "sunset"). They receive one parameter in addition to $self, a "DateTime" object. They return another
"DateTime" object, for the same day, but with the time of the sunrise or sunset, respectively.

sunrise_sunset_span
This method applies to "DateTime::Event::Sunrise" objects. It accepts a "DateTime" object as the second
parameter. It returns a "DateTime::Span" object, beginning at sunrise and ending at sunset.

is_polar_night, is_polar_day, is_day_and_night
These methods apply to "DateTime::Event::Sunrise" objects. They accept a "DateTime" object as the second
parameter. They return a boolean indicating the following condutions:

• is_polar_night is true when the sun stays under the horizon. Or rather under the altitude parameter
used when the "DateTime::Event::Sunrise" object was created.

• is_polar_day is true when the sun stays above the horizon, resulting in a "Midnight sun". Or rather
when it stays above the altitude parameter used when the "DateTime::Event::Sunrise" object was
created.

• is_day_and_night is true when neither is_polar_day, nor is_polar_night are true.

next current previous contains as_list iterator
See DateTime::Set.

EXTENDED EXAMPLES

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

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

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

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

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

         # iterator
         my $dt_span = DateTime::Span->new( start =>$dt, 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',
                              precise   => '1'

         );

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

NOTES

Longitude Signs
Remember, contrary to the usual convention,

EASTERN longitudes are POSITIVE,

WESTERN longitudes are NEGATIVE.

On the other hand, the latitude signs follow the usual convention:

Northen latitudes are positive,

Southern latitudes are negative.

Sun Height
There are a number of sun heights to choose 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 the sun
height 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 the Precise Algorithm
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 select the precise
variant of the algorithm. 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.

Notes on polar locations
If the location is beyond either polar circle, and if the date is near either solstice, there can be
midnight sun or polar night. In this case, there is neither sunrise nor sunset, and the module "carp"s
that the sun never rises or never sets. Then, it returns the time at which the sun is at its highest or
lowest point.

DEPENDENCIES

       This module requires:

       •   DateTime

       •   DateTime::Set

       •   DateTime::Span

       •   Params::Validate

       •   Set::Infinite

       •   POSIX

       •   Math::Trig

BUGS AND CAVEATS

       Using  a  latitude  of  90  degrees (North Pole or South Pole) gives curious results.  I guess that it is
       linked with a ambiguous value resulting from a 0/0 computation.

       Using a longitude of 177 degrees, or any longitude near the 180 meridian, may also give curious  results,
       especially with the precise algorithm.

       The precise algorithm should be overhauled.

AUTHORS

       Original author: Ron Hill <rkhill@firstlight.net>

       Co-maintainer: Jean Forget <JFORGET@cpan.org>

SPECIAL THANKS

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

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

CREDITS

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

       Rich Bowen (rbowen@rbowen.com)
           for suggestions.

       People at <http://geocoder.opencagedata.com/>
           for noticing an endless loop condition in Astro::Sunrise and for fixing it.

COPYRIGHT and LICENSE

   Perl Module
       This  program  is  distributed under the same terms as Perl 5.16.3: GNU Public License version 1 or later
       and Perl Artistic License

       You    can    find    the    text    of    the    licenses    in    the    LICENSE     file     or     at
       <http://www.perlfoundation.org/artistic_license_1_0> and <http://www.gnu.org/licenses/gpl-1.0.html>.

       Here is the summary of GPL:

       This  program  is  free  software;  you  can  redistribute it and/or modify it under the terms of the GNU
       General Public License as published by the Free Software  Foundation;  either  version  1,  or  (at  your
       option) any later version.

       This  program  is  distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
       the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General  Public
       License for more details.

       You  should have received a copy of the GNU General Public License along with this program; if not, write
       to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.

   Original C program
       Here is the copyright information provided by Paul Schlyter for the original C program:

       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.