[Radiance-general] Calculation of solar declination in sun.c

[Richard Mistrick]

I'm not certain why it is 368, but this equation has been in this format in the IES Lighting Handbook for many years.

Rick

From: Martin Gut [mailto:gut at Transsolar.com]
Sent: Thursday, December 17, 2015 6:05 AM
To: radiance-general at radiance-online.org
Subject: [Radiance-general] Calculation of solar declination in sun.c


Dear Radiance Experts,

I have two questions regarding the calculation of solar declination:


1.       Why has the year in function sdec  in  file sun.c  368 days instead of 365 as in the original formula from Cooper ?

return( 0.4093 * sin( (2*PI/368) * (jd - 81) ) )

https://github.com/NREL/Radiance/blob/master/src/gen/sun.c


2.       Why does Radiance not use a better formula, which takes into account, that the Earth orbit is not a circle?

With today computing power, there is no more reason to use this simple formula

Thanks in advance


Martin



Dipl.-Ing. (FH) Martin Gut
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