Day Length Calculator (Sun Duration)
Professional solar cycle dashboard. Calculate precise Sunrise, Sunset, Golden Hour, and Shadow Ratios for any location worldwide. Includes visual daylight timeline.
Configuration
About
This utility provides engineering-grade solar data for professionals in photography, agriculture, and logistics. Unlike basic weather apps, it computes the Astronomical, Nautical, and Civil twilight phases using high-precision trigonometric algorithms. It answers the critical question: How much usable light is available at specific coordinates on a specific date?
We define the Day Length T as the duration between the instant the upper limb of the Sun appears on the horizon and the instant it disappears, adjusted for atmospheric refraction R (≈ 34 arcminutes). The calculations utilize the Local Hour Angle LHA derived from the observer's latitude φ and solar declination δ.
Formulas
The core logic utilizes the Sunrise Equation. The hour angle ωo is calculated as:
Where a is the altitude of the sun (e.g., −0.833° for sunrise). The Shadow Length S for an object of height H is derived from the solar altitude angle α:
Reference Data
| Solar Phase | Sun Angle θ | Lux lx | Utility Case |
|---|---|---|---|
| Solar Noon | MAX | 100,000 | Maximum PV energy generation. Shortest shadows. |
| Golden Hour | 6° to −4° | 500 | Cinematography, landscape photography (warm tones). |
| Civil Twilight | −0.83° to −6° | 300 | Construction work ends. Streetlights activate. |
| Blue Hour | −4° to −8° | 10 | Cityscape photography (cool tones). |
| Nautical Twilight | −6° to −12° | 1 | Horizon visible at sea. Navigation possible. |
| Astronomical Twilight | −12° to −18° | 0.001 | Deep sky observation begins. Faint stars visible. |