Seasons and sky
Day Length
Direct answer
Day Length is the interval between defined sunrise and sunset for a location and date, shaped mainly by latitude, season, and the adopted rise-and-set convention.
Day Length is the elapsed time from local sunrise to local sunset.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Astronomical Season, Meteorological Season, Equinox, Solstice
Day Length is the elapsed time from local sunrise to local sunset.
A Sun-Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.
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The story behind Day Length
Comparing changing daylight has guided calendars and seasonal work since long before precise clocks.
Why Day Length matters
Day length is one of the clearest seasonal signals and affects ecosystems, agriculture, energy use, and daily routines.
Day Length in practice: an example
Near an equinox, calculated daylight can still exceed twelve hours because sunrise and sunset use the Sun's upper edge and include refraction.
Where readings of Day Length go wrong
The usual misreading is to report one day length for an entire country or confuse daylight with sunshine duration under clouds.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Length of Day and Night at the Equinoxes - Official explanation of equinox geometry and why observed daylight is not exactly twelve hours.
- U.S. Naval Observatory: Astronomical Information Center - Official index for time, calendars, seasons, coordinates, and observable sky phenomena.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Last updated
- 2026-09-26
Track changing daylight
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Common questions
What is a day length?
Day Length is the interval between defined sunrise and sunset for a location and date, shaped mainly by latitude, season, and the adopted rise-and-set convention.
What do people get wrong about a day length?
The usual misreading is to report one day length for an entire country or confuse daylight with sunshine duration under clouds.
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