Sunset Calculator

How Sunset Calculator Works?

The Sunset Calculator estimates the Sun's daily position from the selected calendar date, latitude, longitude, UTC offset, and elevation. It calculates the Sun's declination, the equation of time, the local solar noon, the hour angle at the horizon, and the resulting sunrise and sunset times.

First, the date is used to estimate the solar declination $\delta$, which describes the Sun's angular position north or south of the celestial equator. A standard approximation uses the day number $N$ of the year:

The calculation also estimates the equation of time, $E$, which accounts for the difference between apparent solar time and the average clock-based solar day. Solar noon is then found from longitude and the supplied UTC offset. With longitude positive east of Greenwich, a commonly used expression is:

Here, time values are expressed in minutes from midnight in the selected local time zone. The sunset and sunrise hour angle is determined from the latitude $\phi$, solar declination, and the solar altitude used for the visible horizon. A standard civil-sunrise/sunset model uses an effective zenith angle near 90.833 degrees to account approximately for the Sun's apparent radius and atmospheric refraction:

Elevation can lower the apparent geometric horizon, allowing the Sun to remain visible slightly longer at higher observation points. The hour angle is converted into time around solar noon:

The calculator reports the resulting local sunrise time, sunset time, daylight duration, solar noon, and sunset azimuth. Daylight duration is the interval between the two calculated events.

Practical Use Cases

Travelers can select a destination's date, coordinates, time-zone offset, and elevation to determine when daylight begins and ends, helping them plan transportation, sightseeing, hikes, and evening arrivals.

Photographers can use sunset time and sunset azimuth to plan golden-hour sessions, choose a camera position, and anticipate whether the Sun will set toward a desired landscape feature.

Astronomers can use sunrise, sunset, daylight duration, and solar noon to schedule observations, estimate the beginning of darker viewing conditions, and compare solar timing at different latitudes.

Outdoor enthusiasts can check the available daylight for camping, cycling, climbing, fishing, or boating and allow enough time to finish activities before sunset.

Researchers and educators can compare seasonal changes in solar noon, daylight duration, and sunset direction across locations using the calculator's latitude, longitude, and date inputs.

Accuracy and Limitations

The calculator provides a practical astronomical estimate based on standard solar-position equations, an apparent sunrise/sunset horizon near 90.833 degrees, the supplied geographic coordinates, UTC offset, and elevation. Results are generally suitable for planning, but the displayed time can differ from an observed event because atmospheric refraction varies with pressure and weather, local hills or buildings may obstruct the horizon, and the calculator does not automatically determine daylight-saving changes from the location. At extreme latitudes or certain dates, the Sun may remain above or below the modeled horizon for the entire day, so a conventional sunrise or sunset time may not exist. The sunset azimuth describes the unobstructed astronomical horizon and may not match the visible direction from a particular site.

Quick Examples