Sunset Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Sunrise, sunset, and daylight are geometry problems wrapped in calendar and clock conventions. Sunset Calculator estimates sunset or dusk time from the solar model used on this page, while separating astronomical geometry from local-horizon effects.

What this calculator does

The Sunset Calculator centers on sunset or dusk time using the fields that are actually present here: Day date (MM/DD/YYYY), Hemisphere, Latitude (φ), Hemisphere, Longitude (λ). Rather than treating every box as an independent input, use the equation below to identify the driving quantities and read the remaining fields as derived or supporting values when appropriate.

How to use it

Enter date/location/UTC offset, then choose sunset, civil, nautical, or astronomical dusk. The selected twilight definition controls the solar zenith used.

How the calculation works

The sunset path uses the same NOAA-style solar geometry as sunrise. The selected dusk type changes zenith: about 90.833° for sunset, 96° for civil dusk, 102° for nautical dusk, and 108° for astronomical dusk. The page also exposes an uncorrected 90° sunset reference.

Example

At the same date and location, civil dusk occurs later than geometric sunset, nautical dusk later still, and astronomical dusk latest because each definition waits for the Sun to be farther below the horizon.

How to interpret the result

Interpret the result according to the selected event: sunset, civil dusk, nautical dusk, or astronomical dusk are different solar-zenith thresholds. Later twilight definitions should occur after ordinary sunset when the event exists, and the entered UTC offset controls the displayed local clock time.

Limitations and notes

Clock time depends on the UTC offset you choose; daylight saving is not inferred. Terrain and local horizon obstruction are not modeled, and polar locations can legitimately have no event on some dates. Treat “No event” as a solar-geometry condition rather than a calculation failure when the Sun never reaches the selected zenith.