NAME

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

SYNOPSIS

`````` use Astro::Sunrise;
#use Astro::Sunrise qw(:constants);

(\$sunrise, \$sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST);
(\$sunrise, \$sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST,ALT);
(\$sunrise, \$sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST,ALT,inter);

\$sunrise = sun_rise(longitude,latitude);
\$sunset = sun_set(longitude,latitude);

\$sunrise = sun_rise(longitude,latitude,ALT);
\$sunset = sun_set(longitude,latitude,ALT);

\$sunrise = sun_rise(longitude,latitude,ALT,day_offset);
\$sunset = sun_set(longitude,latitude,ALT,day_offset);``````

DESCRIPTION

This module will return the sunrise/sunset for a given day.

`````` 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, including symbolic constants for each.

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, DEFAULT

Sun's supper limb touches the horizon; atmospheric refraction accounted for

-6 degrees, CIVIL

Civil twilight (one can no longer read outside without artificial illumination)

-12 degrees, NAUTICAL

Nautical twilight (navigation using a sea horizon no longer possible)

-15 degrees, AMATEUR

Amateur astronomical twilight (the sky is dark enough for most astronomical observations)

-18 degrees, ASTRONOMICAL

Astronomical twilight (the sky is completely dark)

USAGE

sunrise
`(\$sunrise, \$sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST);`
`(\$sunrise, \$sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST,ALT);`

Returns the sunrise and sunset times, in HH:MM format. (Note: Time Zone is the offset from GMT and DST is daylight savings time, 1 means DST is in effect and 0 is not). In the first form, a default altitude of -.0833 is used. In the second form, the altitude is specified as the last argument. Note that adding 1 to the Time Zone during DST and specifying DST as 0 is the same as indicating the Time Zone correctly and specifying DST as 1.

Notes on Iteration
(\$sunrise, \$sunset) = sunrise(YYYY,MM,DD,longitude,latitude,Time Zone,DST,ALT,inter);

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.

For Example
`````` (\$sunrise, \$sunset) = sunrise( 2001, 3, 10, 17.384, 98.625, -5, 0 );
(\$sunrise, \$sunset) = sunrise( 2002, 10, 14, -105.181, 41.324, -7, 1, -18);
(\$sunrise, \$sunset) = sunrise( 2002, 10, 14, -105.181, 41.324, -7, 1, -18, 1);
=back``````
sun_rise
`\$sun_rise = sun_rise( longitude, latitude );`
`\$sun_rise = sun_rise( longitude, latitude, ALT );`
`\$sun_rise = sun_rise( longitude, latitude, ALT, day_offset );`

Returns the sun rise time for the given location. The first form uses today's date (from DateTime) and the default altitude. The second form adds specifying a custom altitude. The third form allows for specifying an integer day offset from today, either positive or negative.

For Example
`````` \$sunrise = sun_rise( -105.181, 41.324 );
\$sunrise = sun_rise( -105.181, 41.324, -15 );
\$sunrise = sun_rise( -105.181, 41.324, -12, +3 );
\$sunrise = sun_rise( -105.181, 41.324, undef, -12);``````
sun_set
`\$sun_set = sun_set( longitude, latitude );`
`\$sun_set = sun_set( longitude, latitude, ALT );`
`\$sun_set = sun_set( longitude, latitude, ALT, day_offset );`

Returns the sun set time for the given location. The first form uses today's date (from DateTime) and the default altitude. The second form adds specifying a custom altitude. The third form allows for specifying an integer day offset from today, either positive or negative.

For Example
`````` \$sunrise = sun_set( -105.181, 41.324 );
\$sunrise = sun_set( -105.181, 41.324, -15 );
\$sunrise = sun_set( -105.181, 41.324, -12, +3 );
\$sunrise = sun_set( -105.181, 41.324, undef, -12);``````

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 For providing code for sun_rise, sun_set sub's Also adding options for different altitudes.

Joshua Hoblitt [jhoblitt@ifa.hawaii.edu] For providing the patch to convert to DateTime

Chris Phillips for providing patch for conversion to local time.

Brian D Foy for providing patch for constants :)

CREDITS

Paul Schlyer, Stockholm, Sweden

for his excellent web page on the subject.

Rich Bowen (rbowen@rbowen.com)

for suggestions

for finding a bug in the conversion to local time

Lightly verified against http://aa.usno.navy.mil/data/docs/RS_OneYear.html

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

perl(1).

2 POD Errors

The following errors were encountered while parsing the POD:

Around line 690:

You forgot a '=back' before '=head1'

You forgot a '=back' before '=head1'

Around line 713:

'=item' outside of any '=over'