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Subject: Re: Day's lenght
Smith_Peter@XXX.XXX
Date: Tue Dec 31 2002 - 14:08:42 EST
Pierre Boucher [mailto:pboucher@XXX.XXX] asked:
> Does anybody know of a formula that would compute for a given
> latitude and a given date the day's length ie. how many hours
> from sunrise to sunset?
For a web page that performs the calculation (and whose source you can
steal code from), see the NOAA page at
http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html .
It has pointers to other Sun calculators and discussions of the formulae
and corrections.
Juergen Giesen has a nice explanation of the geometry of the problem at
http://www.jgiesen.de/astro/solarday.htm . The page also points to other
pages which contain Java applets to perform this and related calculation.
However, this being a group emphasizing traditional methods, you should
look at http://www.uwsp.edu/physastr/rislove/astrolabe/suncrss.htm,
which shows how to solve the problem using an astrolabe.
-- Peter
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