This code computes sunrise and sunset times. There is a library and an assortment of utilities. The most useful utility is x10events. This program parses crontab files and updates the time fields to track sun events given instructions in the comments.
Combined with an X10 interface like HEYU or X10 this allows the scheduling lighting events that follow the changing seasons and DST automatically. This application does not depend on X10, it can be used for any crontab entry you like.
It is a port of some BASIC code by Roger W. Sinnott for the August 1994 Sky & Telescope that I found on their website: http://www.skypub.com/resources/software/basic/programs/sunup.bas
I apologize for the inscrutability of the code, but I used the same opaque variable names used in the BASIC code to make debugging during the port more reasonable.
riseset.mat is a massaged version of riseset.txt:the official sunrise and sunset times for Cambridge, Massachusetts, USA, 71:07W, 42:22N for the year 1999 from the U.S. Naval Observatory website at: http://aa.usno.navy.mil/AA/data/docs/RS_OneYear.html
There are several programs: today, year, x10events.
'today' simply prints the time and azimuth of today's sunrise and sunset.
'year' prints an entire year's worth of sunrise and sunset times. The companion script year.sh uses year, the table riseset.mat, and gnuplot to generate a verification plot.
'x10events' is really the whole point of all this work. It takes a crontab file that is assumed to contain trailing information about when the events are supposed to happen relative to sunrise and sunset events and generates a new table containing the correct times. I use this to update my heyu timers by placing the script x10events.sh in /etc/cron.daily. 'x10events' assumes that all entries in the crontab are events that it should manage - I suggest placing these events in a separate crontab file - see the FAQ for a more detailed example.
All programs take three arguments: latitude longitude and timezone. All values should be expressed as decimal values, not H:M:S. Latitute is positive North of the equator. Longitude is positive East of the prime meridian. Timezones are positive East of UTC and should be expressed in hours for Standard Time. Do not include Daylight Savings Time offsets.
If the arguments are omited the defaults "42.3778343 -71.1063232 -5" are used. Those correspond to Cambridge MA USA, EST.
The package has been tested and successfully builds and runs under Redhat 5.2, 6.0, 6.2, and 7.2, OSF1 V4.0 (CXX=g++), IRIX64 6.4 (CXX=CC), and IRIX 6.5 (CXX=CC).
The web page is http://www.drwren.com/ephem/
Christopher R. Wren
c@drwren.com