= Daily mean solar irradiance
{title2=$\overline S=(S_0/\pi)(H_0\sin\phi\sin\delta+\cos\phi\cos\delta\sin H_0)$}
At latitude $\phi$ and solar declination $\delta$, integrate $S_0\max(0,\sin\phi\sin\delta+\cos\phi\cos\delta\cos H)$ over hour angle $H$. Sunset occurs at $H_0=\arccos(-\tan\phi\tan\delta)$ when this lies in $[0,\pi]$, with clipping for polar day or night. The displayed daily mean is at the top of the atmosphere; local absorbed <heat flux> also includes transmission and <surface albedo>.
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