Lab 3, Part 2

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Daylight Hours Length of daylight (in addition to solar intensity) is another principal factor that determines solar radiation receipt on earth. Circle of illumination – any given time half of the earth is illuminated by the sun. Daylight length changes daily throughout the year for every location not on the equator So, solar radiation exposure time, like solar intensity, is not distributed uniformly on earth. Except on the equinoxes (everywhere receives 12 hrs of days and 12 hrs of night).

Yearly daylight hrs – equator; 30 o N; 60 o N

Solar angle; azimuth; daylight hours

Solstices Earth – Sun Geometry at 40 o N: Solstices Sun has it’s longest arc… Rises North of East Sets North of West

Solstices Earth – Sun Geometry at 40 o N: Solstices Sun has it’s shortest arc… Rises South of East Sets South of West

Equinoxes Earth – Sun Geometry at 40 o N: Equinoxes Equinoxes: –Midway between solstices Autumnal equinox – September 22 or 23 Vernal equinox – March 21 or 22 Sun arc is “normal”… Rises in the East Sets in the West

Length of daylight LatitudeSummer solsticeWinter SolsticeEquinoxes 0°0°12 hours 10°12 hr 35 min11 hr 25 min12 hours 20°13 hr 12 min10 hr 48 min12 hours 30°13 hr 56 min10 hr 04 min12 hours 40°14 hr 52 min9 hr 08 min12 hours 50°16 hr 18 min7 hr 42 min12 hours 60°18 hr 27 min5 hr 33 min12 hours 70°2 months0 hr 00 min12 hours 80°4 months0 hr 00 min12 hours 90°6 months0 hr 00 min12 hours longer days in summer shorter days in winter