Daylight Calculator

How Daylight Calculator Works?

The Daylight Calculator estimates the Sun's position for a selected calendar date and geographic location. It uses latitude, longitude, the UTC offset, and observer elevation to determine sunrise, sunset, solar noon, daylight duration, and the boundaries of civil, nautical, and astronomical twilight.

The solar declination, which describes the Sun's north–south position relative to the equator, varies throughout the year. A common approximation is:

Here, δ is solar declination and N is the day number in the year. The calculator combines this value with the observer's latitude to find the Sun's hour angle, which represents how far the Earth must rotate before the Sun reaches a specified altitude.

In this equation, φ is latitude, h is the selected solar altitude, and H is the resulting hour angle. Sunrise and sunset use a slightly negative altitude to account for atmospheric refraction and the Sun's visible disk. Twilight calculations use standard solar-altitude thresholds.

Solar noon is calculated from the Sun's apparent transit across the local meridian. Longitude determines the geographic timing of this event, while the UTC offset expresses the result as local clock time. Daylight duration is the interval between sunrise and sunset, and daylight percentage is calculated as:

Elevation can adjust the effective horizon because an observer above sea level can see the Sun slightly earlier at sunrise and slightly later at sunset.

Practical Use Cases

Astronomers can use astronomical dawn and dusk to identify the portion of the night suitable for observing faint celestial objects, while solar noon provides a reference for the Sun's highest daily position.

Photographers can plan golden-hour and blue-hour sessions by reviewing sunrise, sunset, and the civil, nautical, and astronomical twilight boundaries for a specific location.

Travelers can estimate how much usable daylight will be available at a destination and schedule sightseeing, driving, or outdoor excursions around local sunrise and sunset.

Farmers and gardeners can compare daylight duration across dates to help plan field work, crop observation, greenhouse routines, and other activities affected by natural light.

Outdoor planners such as hikers, campers, event organizers, and safety coordinators can select start and finish times that provide adequate daylight and twilight visibility.

Marine navigators can use nautical dawn and dusk to identify periods when the horizon is becoming visible or disappearing, supporting route planning and visual observations.

Accuracy and Limitations

The calculator provides an astronomical estimate based on date, latitude, longitude, UTC offset, and elevation, with standard solar-altitude definitions for sunrise and the three twilight categories. Results are typically suitable for planning, but actual times can differ because of atmospheric refraction, local terrain, weather, and horizon obstructions. Near the Arctic and Antarctic Circles, the Sun may not cross a selected altitude, so sunrise, sunset, or some twilight events may be unavailable during certain seasons. The UTC offset must be selected correctly, including any applicable seasonal clock change; the calculator does not determine civil time-zone or daylight-saving rules automatically. Elevation improves the horizon estimate but does not model detailed surrounding topography.

Quick Examples