Real-World Use Cases

If you are planning a wedding in Edinburgh in October, knowing you have only 10 hours and 20 minutes of daylight helps you schedule the outdoor ceremony early enough to catch golden hour for photos. A day length calculator gives you the exact window so you can build the run sheet around it.

Solar panel installers use day length data to estimate energy production. A 6kW rooftop system in Munich generates roughly four times more electricity in June (16 hours of daylight) than in December (8 hours). The yearly chart lets you see the production curve at a glance and size battery storage accordingly.

Photographers chasing the midnight sun in Tromso, Norway need to know when the sun stops setting. Above the Arctic Circle, day length exceeds 24 hours for weeks in summer. The calculator shows the transition date so you can book your trip during the period of continuous daylight.

Long-distance hikers and ultrarunners plan their start times around available daylight. A runner attempting the 96-mile West Highland Way in September needs to know they have about 12.5 hours of usable daylight, which means a 5am start to finish before dark. The calculator turns the abstract seasonal light into a concrete time budget.

Film location scouts use day length to plan shoot schedules. A commercial shot in Reykjavik in January has only 4 hours and 8 minutes of natural light, meaning most of the shoot day requires artificial lighting. Knowing this in advance lets the production team budget for generators and crew overtime.

How It Works

The calculator uses the SunCalc library, which applies standard NOAA solar position algorithms to compute sunrise and sunset for any latitude, longitude, and date. Day length is the time between sunrise and sunset, measured to the minute.

Sunrise is defined as the moment the upper edge of the sun appears above the horizon, accounting for atmospheric refraction (the sun appears about 0.833 degrees higher than it actually is). Sunset is the reverse: the moment the upper edge disappears below the horizon. The difference between these two moments is the day length.

The yearly chart samples day length on the 15th of each month and plots it as a curve. This shows the seasonal swing: a sinusoidal pattern with peaks near the June solstice (longest day) and troughs near the December solstice (shortest day). The amplitude of the curve depends on latitude: equatorial locations have a nearly flat line near 12 hours, while polar locations swing from zero to 24 hours.

Twilight durations are also calculated. Civil twilight (sun 0 to 6 degrees below horizon) adds usable outdoor light before sunrise and after sunset. Nautical and astronomical twilight extend the visible sky further. The calculator shows each twilight phase so you can plan activities that need some natural light but not direct sunlight.

Step-by-Step Usage Guide

  1. Select a city from the preset list, or enter custom latitude and longitude coordinates for any location on Earth.
  2. Click 'Use my location' to auto-fill coordinates from your device's GPS if available.
  3. Pick a date using the date picker. The calculator defaults to today.
  4. Read the day length display showing hours and minutes of sunlight for that date and location.
  5. Scroll down to the yearly chart to see how day length varies across all 12 months for this latitude, with the selected date marked.
  6. Check the twilight section to see how much usable light extends before sunrise and after sunset.
  7. Compare the selected date against the longest and shortest days of the year to understand where it falls in the seasonal cycle.

Examples

Input

New York (40.71N), July 18, 2026

Output

14h 53m of daylight, sunrise 5:38am, sunset 8:31pm

Near the summer peak; longest day was June 21 at 15h 05m

Input

New York (40.71N), December 21, 2026

Output

9h 15m of daylight, sunrise 7:17am, sunset 4:32pm

Shortest day of the year for the Northern Hemisphere

Input

Singapore (1.35N), July 18, 2026

Output

12h 10m of daylight, sunrise 7:02am, sunset 7:12pm

Near the equator, day length stays close to 12 hours all year

Input

Tromso, Norway (69.65N), July 18, 2026

Output

24h 00m of daylight (midnight sun)

Above the Arctic Circle, the sun never sets from mid-May to mid-July

Input

Tromso, Norway (69.65N), December 21, 2026

Output

0h 00m of daylight (polar night)

The sun never rises; only nautical twilight provides any daylight glow

Input

Sydney, Australia (-33.87S), July 18, 2026

Output

10h 08m of daylight, sunrise 6:56am, sunset 5:04pm

Winter in the Southern Hemisphere; shortest day was June 21 at 9h 54m

Common Mistakes and Edge Cases

Things to watch out for

  • Day length is not the same as usable daylight: Civil twilight adds roughly 30 minutes of usable outdoor light before sunrise and after sunset. If you need total visible light, add twilight time to the day length.
  • Polar regions have zero or 24-hour day length: Above the Arctic Circle (66.55N) and below the Antarctic Circle (66.55S), the sun does not rise or set for periods around the solstices. The calculator shows 0h 00m or 24h 00m during these periods.
  • Day length varies with latitude, not longitude: Two cities at the same latitude (e.g., Madrid and New York, both around 40 degrees) have nearly identical day lengths on the same date, despite being in different time zones. Longitude affects sunrise/sunset clock times, not the duration between them.
  • The equinox is not exactly 12 hours everywhere: On the equinox, the center of the sun is above the horizon for exactly 12 hours, but because sunrise is defined by the upper edge and refraction lifts the sun, measured day length is typically 12 hours and 7 to 8 minutes on the equinox.
  • Elevation affects sunrise/sunset slightly: At high altitude, you can see the sun earlier over the horizon. The calculator uses sea-level refraction, so mountain locations may get a few extra minutes of daylight.
  • Daylight saving time shifts clock times but not day length: When DST starts or ends, sunrise and sunset shift by one hour on the clock, but the actual duration of sunlight does not change.
  • The chart uses monthly samples: The yearly chart plots day length on the 15th of each month. The actual curve is smooth, but solstice peaks may fall on the 21st, so the chart slightly underestimates the extremes.

FAQ

What is day length?

Day length is the time between sunrise and sunset, when the sun is above the horizon. It is measured in hours and minutes. At the equator, day length stays close to 12 hours year-round. At higher latitudes, it varies dramatically with the seasons, from very long days in summer to very short days in winter.

Why does day length change throughout the year?

Earth's axis is tilted 23.44 degrees relative to its orbit around the sun. This tilt means different latitudes receive more or less direct sunlight at different times of year. During the June solstice, the Northern Hemisphere leans toward the sun and gets its longest days. During the December solstice, it leans away and gets its shortest days. The Southern Hemisphere is reversed.

What is the longest day of the year?

In the Northern Hemisphere, the longest day falls on or near June 21 (the June solstice). In the Southern Hemisphere, it falls on or near December 21. The exact length depends on latitude: at 40 degrees north, the longest day is about 15 hours. At 60 degrees north, it is about 18.5 hours. Above the Arctic Circle, the sun does not set at all.

What is the shortest day of the year?

In the Northern Hemisphere, the shortest day falls on or near December 21 (the December solstice). At 40 degrees north, the shortest day is about 9 hours and 15 minutes. At 60 degrees north, it is about 5.5 hours. Above the Arctic Circle, the sun does not rise at all during the polar night period.

Why is the equinox day not exactly 12 hours?

Sunrise is defined as the moment the upper edge of the sun appears above the horizon, and sunset is when the upper edge disappears. Because the sun has a visible diameter of about 0.5 degrees and atmospheric refraction lifts it by about 0.833 degrees, the sun is visible for slightly longer than 12 hours on the equinox. The actual 12-hour day occurs a few days before the spring equinox and a few days after the autumn equinox.

How accurate is the day length calculation?

The calculator uses the SunCalc library with NOAA-standard solar position algorithms. Results are accurate to within one minute for most locations at sea level. High-altitude locations may see slightly longer day length because the horizon is lower. The calculation does not account for local terrain blocking the horizon (mountains, buildings).

What is the difference between day length and twilight?

Day length measures only the time the sun is above the horizon. Twilight is the period after sunset or before sunrise when the sun is just below the horizon but still illuminates the sky. Civil twilight (sun 0 to 6 degrees below horizon) provides enough light for most outdoor activities. Nautical and astronomical twilight are progressively darker.

Can I calculate day length for any location on Earth?

Yes. Enter the latitude and longitude for any location. The calculator handles all latitudes from 90N to 90S, including polar regions where day length can be 0 or 24 hours during solstice periods.

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Data Sources and Accuracy

  • SunCalc library - implements NOAA solar position algorithms for sunrise, sunset, and twilight calculations
  • Earth axial tilt: 23.44 degrees (IAU 1976 value, still current as of 2026)
  • Atmospheric refraction: 0.833 degrees (standard NOAA value for sea-level horizon)
  • Solar declination computed from the date using the standard astronomical formula

Day length calculations are accurate to within one minute for sea-level locations with a flat horizon. Mountainous terrain, high altitude, and atmospheric conditions (temperature, pressure) can shift sunrise and sunset by a few minutes. The yearly chart uses monthly samples (15th of each month) and may slightly underestimate solstice extremes. For navigation or aviation, use certified ephemeris data.