Linked astronomy tools
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 the twilight and sun event calculator effectively
Enter the observing date, latitude, longitude, and timezone before reading sunrise, sunset, and twilight intervals. The results depend strongly on location and date, especially at high latitudes.
How it works
The calculator estimates the sun's altitude through the day and finds crossings for sunrise, sunset, and civil, nautical, and astronomical twilight thresholds. Horizon correction adjusts the effective horizon, so terrain or buildings can be modeled as a simplified offset.
When to use
Use this page for observing plans, photography timing, outdoor scheduling, and classroom checks. Near polar day or polar night, some events may not exist on the selected date; the page should be read as an event-status report, not just a timetable.
Common mistakes to avoid
- Using the wrong timezone for the selected longitude.
- Reversing east/west longitude signs.
- Assuming every date and latitude has both sunrise and sunset.
- Confusing civil, nautical, and astronomical twilight thresholds.
Interpretation and worked example
Start with horizon correction set to zero. If a local obstruction matters, raise the horizon and compare how sunrise becomes later or sunset becomes earlier. If an event is missing, check whether the sun never crosses that altitude threshold on the selected date.
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.