Wndsn Sun Calculator
Companion to Wndsn Quadrant Telemeters: Low tech, high utility graphical distance computers from the Wndsn applied science lab.
By way of using a Wndsn Quadrant to measure local latitude and calculate declination for a given date, a number of values can be derived through further Quadrant computations.
The celestial sphere with all relevant variables showing the relationship between the equatorial and azimuthal coordinate system, source: GQT5
Input
Formulas
[Load sample values (JSON) (XML) (CSV).]
- H(φ,δ)
- Sun altitude at noon H from latitude:
H = (90° − φ) + δ - αsr(φ,δ)
- Azimuth αsr of rising/setting Sun:
cos αsr = sin δ / cos φ - τsr(φ,δ)
- Hour angle τsr of rising/setting Sun (from noon):
cos τsr = -tan φ · tan δ[To offset refraction, for true sunrise/set, a constant of 1.66667° is added to the result.] - τ(h,φ,δ)
- Hour angle τ from instantaneous Sun altitude h:
cos τ = (sin h - sin δ · sin φ) / (cos δ · cos φ) - αs(τ,φ,δ)
- Sun azimuth αs for a given hour:
tan αs = sin τ / (sin φ · cos τ - cos φ · tan δ)
where H = Sun altitude at noon, h = instantaneous Sun altitude, τ = hour angle, φ = latitude, and δ = declination.
Notes
- For certain locations, such as Sevilla in Spain, which is located at 6°W but belongs to the "wrong" timezone CET (UTC+1), the results returned may be partially wrong, since Tycho calculates from true longitude only.