Example

Find the solar altitude and azimuth angles at 2 h after local noon on June 15 for a city located at 40°N latitude. Also find the sunrise and sunset hours and the day length.

Solution

From Eq. (2.5), the declination on June 15 (N = 167) is

From Eq. (2.8), the hour angle, 2 h after local solar noon is h = +0.25(120) = 30° From Eq. (2.12), the solar altitude angle is sin(a) = sin(40) sin(23.35) + cos(40) cos(23.35) cos(30) = 0.864 Therefore, a = 59.75°

From Eq. (2.13), the solar azimuth angle is sin(30)

cos(59.75)

0.911

Day length = 2/15 cos_1[-tan(40)tan(23.35)] = 14.83h

This means that the sun rises at 12 - 7.4 = 4.6 = 4:36 am solar time and sets at 7.4 = 7:24 pm solar time.

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