1. Set the date range: "Start date" and "End date" define the period to compare (maximum one year). The current year is set by default.
2. Choose the first city (City A): click the yellow map, drag the marker, or search a city by name. Give it a short legend name if you wish.
3. Choose the second city (City B) on the red map, the same way.
4. Watch the animated chart: in 30 seconds it draws two overlapping curves. The vertical distance between the curves is the difference in daylight hours that day.
5. Share the comparison with the 🔗 Share button: you get a link that reproduces the same chart on any device.

The tool applies the official NOAA (National Oceanic and Atmospheric Administration) solar algorithm to each of the two cities. For each day in the interval, it calculates sunrise and sunset in the city's local time zone and from these derives day length as the difference sunset − sunrise. Typical accuracy is within one minute for latitudes between -60° and +60°.

The two series — one for City A and one for City B — are overlaid on the same chart. The vertical distance between the curves on a given day represents the difference in day length between the two locations. If the cities are in different hemispheres the curves appear mirrored; if they're at the same latitude the curves nearly coincide.

The chart shows two lines: yellow for City A, red for City B. The vertical axis represents day length (0-24 hours), the horizontal axis the dates. The date axis automatically adapts ticks to the interval length: monthly for a full year, every 2 weeks for medium periods, daily for short intervals.

When you change data, the chart rebuilds in 30 seconds. Play/Pause, Reset and the speed buttons ½× · 1× · 2× let you navigate the animation. During the animation, a line below the chart shows current date, day length of both cities, and absolute difference Δ.

One of the most common questions for those planning winter travel, relocations, or outdoor activities. Visual comparison makes obvious what numbers alone don't tell:

• Oslo vs Palermo in December: Palermo has about 9h 34m of daylight at the winter solstice, Oslo only 5h 54m. Almost four hours' difference per day.
• Stockholm vs Canary Islands: in December Tenerife exceeds 10h 30m of daylight, Stockholm barely 6h. Try the comparison and see how the two curves only converge at the equinoxes.
• London vs Athens: Athens gains nearly 2 hours of daylight per day over London in winter months. The difference vanishes in spring and autumn.
• New York vs Miami: Miami has about 1h 17m more daylight than New York at the winter solstice — relevant for Americans planning a winter getaway south.

For climate tourism, psychological well-being (vitamin D metabolism), and outdoor activity planning, these differences are decisive. Enter the two cities in the comparison above and watch the curves.

As Earth orbits the Sun, the two hemispheres receive light in opposite patterns: while the North enjoys long summer days, the South experiences short winter days, and vice versa. If you compare New York with Sydney, the two curves mirror each other throughout the year.

Extreme differences occur at the solstices (June 21 and December 21), when one city has its longest day and the other its shortest. At the equinoxes (March 20-21 and September 22-23) the two curves meet around 12 hours, because those two days have practically equal day length everywhere on Earth.

An extreme case: compare Reykjavík (64° N) with Punta Arenas (53° S) — the daylight swing is enormous in both, but perfectly inverted in time.

• New York vs Stockholm — in summer Stockholm exceeds New York by about 3 hours of daylight per day.
• London vs Sydney — mirrored curves, maximum difference at the solstices.
• Quito vs Reykjavík — Quito sits on the equator and has ~12 hours of daylight all year (almost flat line); Reykjavík swings wildly between ~4 and ~21 hours.
• Singapore vs any other city — Singapore is just a few degrees from the equator and always has about 12 hours of daylight, regardless of season.
• Tromsø vs Tromsø same place, different dates: see the transition from polar night to midnight sun drawn as a steep ramp.
• New York vs Madrid — same latitude (~40° N), same daylight hours: the two curves are practically overlapping.

If you need detailed data for one location only (with sunrise, sunset, day length, night length, and the three twilights — civil, nautical, astronomical), use the free sunrise sunset calculator.