Calculator Inputs
Formula Used
Daylight duration: D = (2 ÷ 15) × cos⁻¹(−tan φ × tan δ)
Solar declination: δ ≈ 23.44° × sin[(360° ÷ 365) × (N − 81)]
Standard sunrise zenith: 90.833°, including refraction and solar radius.
Latitude and declination determine the daily solar hour angle. Longitude and time settings convert events into local clock times. Shading adjustments estimate usable exposure for practical planning.
How to Use
Choose one date or select a longer analysis period. Enter coordinates, time offset, shading, and surface details. Submit the form to compare daylight and usable sunlight.
- Select a date, month, year, or custom range.
- Enter accurate latitude, longitude, and UTC offset.
- Add shade, cloud, horizon, and panel information.
- Review daylight, twilight, peak sun, and classification results.
- Copy, print, or export the completed calculation.
Example Data
| Location | Date | Latitude | Longitude | UTC offset | Suggested use |
|---|---|---|---|---|---|
| Karachi | 21 June | 24.8607° | 67.0011° | +5 | Garden and solar planning |
| London | 21 June | 51.5074° | -0.1278° | 0 or +1 | Long summer daylight |
| Sydney | 21 December | -33.8688° | 151.2093° | +10 or +11 | Southern summer comparison |
Accuracy and Limitations
Astronomical results use standard solar geometry and refraction assumptions. Weather, terrain, trees, and buildings can change observed sunlight. Site measurements provide the strongest local planning confirmation.
Frequently Asked Questions
What is the difference between daylight and sunshine?
Daylight covers sunrise through sunset. Sunshine requires direct solar visibility. Clouds and obstacles reduce usable sunshine considerably.
What are peak sun hours?
Peak sun hours express equivalent strong solar exposure. They differ from total daylight duration. Solar projects commonly use this practical energy measure.
Why is sunrise based on 90.833 degrees?
The angle includes atmospheric refraction and solar radius. It matches common sunrise calculation practice. Local terrain can still delay visible sunrise.
How does horizon obstruction affect sunlight?
Obstructions raise the effective visible horizon. Sunrise becomes later and sunset becomes earlier. Mountains and buildings can create large differences.
Can this calculator classify garden sunlight?
Yes, it estimates effective direct exposure. Results use common sunlight classification ranges. Observe seasonal shade before selecting sensitive plants.
Does cloud cover change astronomical daylight?
No, clouds do not change sunrise geometry. They reduce effective sunlight and solar energy. Enter cloud reduction for practical exposure estimates.
What causes polar day or polar night?
Earth's axial tilt creates extreme seasonal daylight. High latitudes may miss sunrise or sunset. The calculator reports these special conditions automatically.
Which panel azimuth should I use?
Equator-facing panels usually receive stronger annual exposure. Southern orientation suits northern latitudes. Northern orientation suits southern latitudes.
Can I analyse an entire year?
Yes, choose the yearly calculation option. The tool limits processing to 367 days. Charts reveal seasonal daylight changes clearly.
Why might local times differ slightly?
Terrain and atmospheric conditions shift visible events. Time-zone rules may also change seasonally. Verify daylight saving settings for accurate clocks.