In the first lab manual exercise you are required to calculate the noon sun angle. To do so you need to know the zenith angle. The zenith angle (Z) is “the number of degrees between a site location and the declination of the Sun.”
To calculate the zenith angle:
- Subtract site location and declination when they are in the same hemisphere. Example: Site location is 60N on June 21st the declination is 23.5N. Z=60 – 23.5 = 36.5
- Add the site location and declination when they are in different hemispheres. Example: Site location is 60N on Dec 22 the declination is 23.5S. Z=60 + 23.5 = 83.5
Then the noon sun angle is:
NSA = 90 – Z
Note in these examples that the declination is subtracted from or added to the site location. There may be a time when the site location has a smaller value than the declination yielding a negative Z.
A site at 3.5 S on Dec 22 (declination 23.5S).
Z = 3.5 S – 23.5 S = -20
Given that we can’t have a negative Z, just make it a positive number. It still is by definition “the number of degrees between a site location and the declination of the Sun.”