What Counts as Sunrise and Sunset?
Sunrise is the moment the upper edge of the Sun’s disc first appears above the horizon. Sunset is the moment it disappears below. These definitions account for atmospheric refraction, the bending of light through the atmosphere, which means the Sun is actually just below the geometric horizon when it appears to touch it. This effect adds a few minutes of daylight at each end of the day.
Because refraction varies with temperature, pressure, and humidity, computed sunrise and sunset times carry an inherent uncertainty of roughly one to two minutes.
Why Times Change Through the Year
The main driver is Earth’s axial tilt: the planet’s rotational axis is tilted about 23.4 degrees from the perpendicular to its orbital plane. As Earth orbits the Sun, this tilt changes which hemisphere leans toward the Sun:
- Around the June solstice, the Northern Hemisphere tilts toward the Sun. The Sun follows a higher, longer arc across the sky, producing longer days and shorter nights.
- Around the December solstice, it tilts away. The Sun’s arc is lower and shorter, producing shorter days and longer nights.
- At the equinoxes (March and September), neither hemisphere is tilted toward the Sun. The Sun rises due east and sets due west, and day and night are approximately equal.
The solstice is the longest (or shortest) day, but it’s not the day with the earliest sunrise or latest sunset. Those are offset by days to weeks because of how Earth’s slightly elliptical orbit shifts the timing of solar noon throughout the year.
How Latitude Affects Day Length
The further you are from the equator, the more dramatic the swing between summer and winter day lengths.
| Latitude | Example | Winter day | Summer day |
|---|---|---|---|
| ~1°N | Singapore | ~12 hours | ~12 hours |
| ~30°N | Houston | ~10 hours | ~14 hours |
| ~40°N | Madrid | ~9.5 hours | ~15 hours |
| ~51°N | London | ~8 hours | ~16.5 hours |
| ~60°N | Helsinki | ~5.5 hours | ~18.5 hours |
At the equator, day length barely changes; sunrise and sunset shift by only about half an hour across the whole year. Near the poles, the variation is total: months of continuous daylight in summer, months of darkness in winter.
How Fast Does Day Length Change?
Not at a constant rate. Day length changes fastest near the equinoxes, gaining or losing two to three minutes per day at mid-latitudes. Near the solstices, the change slows to just seconds per day. This is why spring and autumn feel like rapid transitions, while the longest and shortest days seem to linger.
Twilight
After sunset (and before sunrise), the sky doesn’t go dark immediately. This transition period is called twilight, and it comes in three stages based on how far the Sun is below the horizon:
| Type | Sun below horizon | What it looks like |
|---|---|---|
| Civil twilight | 0°–6° | Bright enough for outdoor activities. Only the brightest stars visible. |
| Nautical twilight | 6°–12° | Horizon still faintly visible. Most stars visible. |
| Astronomical twilight | 12°–18° | Sky nearly fully dark. Beyond 18° is full night. |
Twilight duration depends on latitude and time of year. Near the equator, the Sun drops steeply below the horizon, so civil twilight lasts only about 20–25 minutes. At higher latitudes, especially in summer, the Sun sets at a shallow angle, stretching twilight for over an hour. At latitudes above roughly 48–49°N in midsummer, astronomical darkness never occurs at all; the sky never gets fully dark.
Common Misconceptions
“The equinox has exactly 12 hours of daylight.” Close, but not quite. Because of atmospheric refraction and the way sunrise is defined (upper edge, not centre), the equinox day is several minutes longer than 12 hours. The date when day and night are truly equal, called the equilux, falls a few days before the March equinox and a few days after the September equinox.
“The Sun always rises due east.” Only at the equinoxes. In summer, it rises north of east and sets north of west (in the Northern Hemisphere). In winter, south of east and south of west. At the solstices, the deviation can be 30 degrees or more at mid-latitudes.
“Earth is closer to the Sun in summer.” Earth is actually closest to the Sun in early January, during Northern Hemisphere winter. Seasons are caused by axial tilt, not distance.
How Airpult Shows Sunrise and Sunset
Airpult displays daily sunrise and sunset times on the forecast page for your location, along with day length. Use the explore page to search for any location and check its sunrise and sunset times.
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