Daylight duration
For a normal rising and setting day, duration is the elapsed time from sunrise to sunset. It is calculated from absolute instants, not by subtracting clock labels.
Long days and short days
Latitude and the season change daylight duration. Near the poles, the Sun can remain above or below the horizon through an entire day. Such days are labeled explicitly.
Hours of daylight from sunrise to sunset
The meter shows the daylight share of a nominal 24-hour cycle. Around the equinoxes every place gets slightly more than twelve hours between sunrise and sunset, because the times refer to the Sun’s upper edge and include refraction; the date when day and night are closest to equal falls a few days away from the equinox itself. The monthly calendar lists daylight for every day of a month.
How fast the day changes
The comparison table sets the selected day against the previous day, seven days earlier and thirty days earlier. Day length changes fastest near the equinoxes and hardly at all near the solstices, and the swings grow with latitude: a city at 60° sees far larger seasonal changes than one at 25°.
Polar day and polar night
Above the polar circles the Sun can stay up for a whole day (24h 00m of daylight) or stay down (0h 00m). The calculator reports these states in words rather than inventing a sunrise or sunset. Twilight boundaries for those days are on the twilight page.