Comments on: Sunrise, Sunset

By: Fredrik

Fredrik — Tue, 16 Feb 2010 11:16:53 +0000

There are public domain APIs to do this. Check the Acknowledgements section on http://sunrisehour.com!

By: programmingpraxis

programmingpraxis — Wed, 25 Nov 2009 21:06:42 +0000

See the article from the U. S. Naval Observatory referenced in the solution. It works even very close to the poles.

By: Kallikanzarid

Kallikanzarid — Wed, 25 Nov 2009 21:02:04 +0000

What about polar circles? How should a program behave when given a point close to a pole?

By: John Cowan

John Cowan — Tue, 24 Nov 2009 20:52:24 +0000

Fair enough, since this is a float API. I was making a general point that was malapropos to this particular piece of code.

By: programmingpraxis

programmingpraxis — Tue, 24 Nov 2009 14:59:25 +0000

The GMT offset need not be given as an integer. Here is the sunrise/sunset calculation for Calcutta, India for today:

> (call-with-values
    (lambda () (solar 22.6 -88.4 2009 11 24 -6.5))
    (lambda (rise set)
      (display "Sunrise: ") (display rise) (newline)
      (display "Sunset: ") (display set)  (newline)))
Sunrise: 5:57
Sunset: 16:53

The times agree with Weather Underground within three minutes.

By: John Cowan

John Cowan — Tue, 24 Nov 2009 14:42:58 +0000

Note that there are places, like central Australia and the whole of India, where the timezone offset from Universal Time is not an integral number of hours. The solution should specify the offset in minutes instead.