Quick answer
Sunrise and sunset are the moments the Sun's upper edge appears to touch a flat horizon. Because the atmosphere bends sunlight and the Sun is a disc rather than a point, they are calculated for the instant the Sun's center is 0.833° below the horizon. Times then depend on your latitude, longitude, the date and your time zone.
Why −0.833°?
The standard definition combines two effects:
- Atmospheric refraction (about 0.57°, or 34 arcminutes). Air bends light from a low Sun upward, so you see the Sun above the horizon when it is geometrically just below it.
- The Sun's radius (about 0.27°, or 16 arcminutes). Sunrise and sunset refer to the Sun's top edge, not its center.
Together they add up to 50 arcminutes, or 0.833°. So when an app says “sunset,” the Sun's geometric center is already slightly below the horizon.
Why your observed sunrise can differ by a few minutes
- Terrain and buildings. A ridge or skyline to the east delays the moment you actually see the Sun; a valley to the west makes it vanish early.
- Elevation. From a mountaintop or a high-rise you can see slightly below the normal horizon, so sunrise comes a little earlier and sunset a little later. Standard calculations, including Dayclipse's, assume an observer at the horizon level.
- Unusual refraction. The 34′ refraction value is an average. Very cold air, temperature inversions or warm water can bend light more or less, shifting times by a minute or more.
- Location within a city. City-level coordinates are a good approximation, but in large or wide regions the exact time can vary slightly across the area.
Why solar noon is rarely at 12:00
Solar noon is the moment the Sun reaches its highest point and crosses due south (or due north in the Southern Hemisphere). Clock time is a convention shared across a whole time zone, so solar noon drifts away from 12:00 because of:
- your longitude relative to the time zone's reference meridian (4 minutes per degree),
- daylight saving time, which shifts clocks by an hour, and
- the equation of time — a seasonal variation of roughly −14 to +16 minutes caused by Earth's tilted axis and elliptical orbit.
For example, for New York on October 18, 2026, Dayclipse shows solar noon at 12:40 PM. Daylight saving time adds an hour, while the city's position just east of its time-zone meridian and the mid-October equation of time each make the Sun peak earlier. Sunrise is at 7:10 AM and sunset at 6:10 PM — about 11 hours of daylight.
Why the earliest sunset isn't on the shortest day
In the mid-northern latitudes of the US and Europe, the shortest day is the December solstice, yet the earliest sunset usually falls in early December and the latest sunrise in early January. The equation of time is changing quickly in that season, sliding the whole day later on the clock, while the length of daylight changes only slowly near the solstice.
When day length changes fastest
Day length changes most quickly around the March and September equinoxes and most slowly around the solstices. The farther you are from the equator, the larger the daily change.
Polar day and polar night
Inside the Arctic and Antarctic Circles there are dates with no sunrise or no sunset at all. In those cases Dayclipse shows that the Sun is up all day or down all day rather than a time.
Next, see how the minutes after sunset are divided: the three types of twilight.