NAME

sscalc — calculate time of sunrise and sunset

SYNOPSIS

DESCRIPTION

sscalc calculates the time of sunrise and sunset for a date and location and prints the results.

In order to calculate the sunrise and sunset, the sscalc program must know the latitude and longitude of your location. You can pass this information to the program via environment variables or via the command line.

To set the longitude via the command line, use the -o option. Similarly, to set the latitude, use the -a option. The number passed must be a floating point representation of the degrees of longitude or latitude. Locations west of the prime meridian are represented as positive numbers, those located east of GMT are negative numbers. North latitudes are positive, while south latitudes are negative. For example, the longitude of Walnut Creek, California, is 122.06 and its latitude is 37.90.

The program will also search the environment for the variables LATITUDE and LONGITUDE. The format of these variables is exactly the same as on the command line.

By default, sscalc will print the sunrise and/or sunset for the current date. You may change the date being calculated by using the -m and -d options to set the month and day. The month must be a number from 1 to 12, while the day must be from 1 to 31. Times are printed out in the default representation for the locale.

To restrict the output, use the -r or -s flag to print only the sunrise or sunset respectively. To print a series of times, use the -n option to pass the number of dates to print out.

EXAMPLES

To print the sunrise and sunset for Acapulco, Mexico on the first day of summer, you'd use

BUGS

The calculations are an approximation and may be wrong by as much as two minutes.

When calculating times for areas above the Arctic or below the Antarctic Circles, the program will report the times for the nearest (chronologically) sunrise and sunset. The year reported will be incorrect sometimes, but the day of year will be correct.

Sunrise and sunset times are calculated internally to GMT, and displayed in the local timezone. If the coordinates given don't match the current timezone setting, expect results that are off by a number of hours.

FILES

Included with the sscalc program is the cities.txt file, which has the latitude and longitude for a whole lot of cities around the world. This file will normally be installed in /usr/local/share/doc/sscalc/cities.txt.

AUTHOR

Keith Walker ⟨kew@icehouse.net⟩ did the port of a web page that at the time of this writing was http://www.srrb.noaa.gov/highlights/sunrise/gen.html. This ported code was released with the permission of the author of the original code, Chris Cornwall.