This is a guide for solar collector use. Section II shows the effective number of sunlit hours per day at the solstices and equinox captured by several solar collector types: stationary flat, sun tracking flat, east-west parabolic and two-trough concentrators and a north-south, sun tracking, two-trough concentrator. Section III introduces the sun direction from the circular orbit earth; it is accurate enough for most applications. Section IV develops atmospheric attenuation of sunlight. Section V puts it all together for the calculated results presented in Sec. II.