This is sscalc, a sunrise/sunset time calculator, ported to C.
You can find the sunrise and sunset times for anywhere in the world
as long as you know the latitude and longitude of the location.

The program is a port of the JavaScript program located at
http://www.srrb.noaa.gov/highlights/sunrise/gen.html

The page was written by Aaron Horiuchi, Chris Lehman and Chris
Cornwall.