Example: zenith angle = (location latitude) (subsolar point) At Phoenix, AZ (33N), on January 20 (subsolar point: 20S) Zenith angle = 33 (20) Zenith angle = 53 At Sao Paulo, Brazil (23S), on January 20 (subsolar point: 20S) Zenith angle = 23 (20) Zenith angle = 3 Absolute value zenith angle = 3