Model scope and corrections — read first
For observer latitude φ and solar declination δ, geometric solar-noon altitude is H = 90° − |φ − δ|. H decreases as |φ − δ| increases, not whenever latitude decreases. H = 90° means the Sun is at the zenith; H = 0° means it is on the horizon, not the sole condition for a non-overhead Sun. H can be negative when the Sun is below the horizon, even if the interface displays only [0°, 90°]. At the North Pole H = δ; at the South Pole H = −δ. A geometric H = 0° boundary satisfies φ = δ ± 90° where the latitude is valid. The overhead Sun occurs once yearly at each tropic and generally twice between the tropics.