How to read A/B codes
Quick start (3 steps)
- Set location, date, and timezone.
- Optionally add horizon correction (degrees).
- Compute to get twilight events, night length, and the daily sun-altitude curve.
Inputs
Results
| sunrise | — |
|---|---|
| sunset | — |
| Solar noon | — |
| Civil dawn / Civil dusk | — / — |
| Nautical dawn / Nautical dusk | — / — |
| Astronomical dawn / Astronomical dusk | — / — |
| Astronomical night length (min) | — |
| Resolved TZ | — |
Sun altitude chart
Definitions & notes
- Azimuth: N=0°, E=90°, S=180°, W=270° (clockwise).
- Altitude: horizon=0°, zenith=+90°, negative below horizon.
- Longitude sign: east positive, west negative.
- Event thresholds: sunrise/set=-0.833°, twilight=-6/-12/-18°.
- Horizon correction shifts event thresholds by the same amount (simple visibility correction).
How to use this calculator effectively
This guide helps you use Twilight, sunrise & sunset calculator in a repeatable way: define a baseline, change one variable at a time, and explain each output using explicit assumptions before sharing results.
How it works
The calculator applies deterministic formulas to your input values and only rounds at the final display layer. This makes it useful for comparative analysis: keep one scenario as a baseline, then vary assumptions and measure the delta in both absolute terms and percentage terms. If a change appears too large or too small, verify units, period conventions, and sign direction before interpreting the result.
When to use
Use this page when you need a fast planning estimate, a classroom check, or a reproducible scenario that teammates can review. It is most effective at the decision-prep stage, where you need to compare options quickly and decide which assumptions deserve deeper modeling or external validation.
Common mistakes to avoid
- Mixing units such as percent vs decimal, or monthly vs yearly settings.
- Changing multiple fields at once, which hides the real cause of result movement.
- Comparing outputs across tools without aligning constants and default conventions.
- Treating rounded display values as exact inputs for downstream calculations.
Interpretation and worked example
Start with a baseline case and save that output. Next, edit one assumption to reflect your realistic alternative, then compare both the direction and size of change. If the direction matches domain intuition and magnitude is plausible, your setup is likely coherent. If not, check hidden defaults, unit conversions, boundary conditions, and date logic before drawing conclusions.
See also
FAQ
Why do sunrise/sunset sometimes show as None?
At high latitudes or near the solstice, the sun may not cross the horizon in one direction on that date. The script keeps the status explicit to avoid silent errors when no event exists.
What are civil, nautical, and astronomical twilight?
Twilight is categorized by sun altitude relative to the horizon. This calculator uses -6°, -12°, and -18° as practical thresholds for bright/blue/astronomical sky phases.
How does horizon correction affect results?
A positive horizon moves the reference line upward, so low-elevation events become harder to satisfy. This models terrain/building obstruction in a simplified way.
What should I enter first?
Start with the minimum required inputs shown above the calculate button, then keep optional settings at their defaults for a first pass. After getting a baseline, change one parameter at a time so you can explain which assumption moved the output.
How precise are the results?
The calculator keeps internal precision and rounds only for display. Small differences can still appear if another tool uses different constants, period conventions, or rounding rules. Align assumptions before comparing final values.