shortday

Shortday is a term used to describe a day in which the amount of daylight is significantly shorter than the typical or average day length for a given location and time of year. The exact threshold for what constitutes a shortday varies by discipline and region, but it generally refers to days with notably reduced sunshine hours, often occurring during the winter months in temperate and higher latitude zones.

Astronomical and geographical context is central to the concept. Shortdays arise from the tilt of the Earth’s axis relative to its orbit around the sun, which causes shorter daylight hours as winter approaches in the northern and southern hemispheres. In equatorial regions, day length remains close to 12 hours year-round, so the practical relevance of shortdays is limited there. Weather conditions such as cloud cover can further affect the perceived amount of daylight on a given day, even when the astronomical daylight duration is fixed.

Impacts and applications of the concept vary by field. In ecology and horticulture, shorter photoperiods influence the timing of biological processes such as flowering in some plants and seasonal behaviors in animals. In human contexts, shortdays can affect energy demand, outdoor activity patterns, and mood for individuals sensitive to seasonal changes. In solar energy planning and building design, longer periods of reduced daylight may influence energy consumption and the optimization of lighting and heating strategies.

See also: daylight hours, photoperiod, polar night, daylight saving time.