[postgis-users] day length calculation

[Kirk Wythers]

I am looking for ideas to add a daylength calculation to a postgis  
database. The database in question has a table named "sites", which  
contains lat, lon, and geometry info for a number of locations. A  
second table contains climate data including a day_of_the_year column.

I would like to add the capability to calculate the length of each  
day (could be done as a view or another table). The equation for day  
length calculation takes as input day_of_the_year and latitude, does  
some trig (uses acos, tan, cos, radians, and pi) and spits out an  
estimate of the day length in hours.

How would folks recommend I approach this problem?

Thanks,

Kirk