Season

Season is one of the four divisions of the year in temperate zones, marked by characteristic weather, temperature ranges, and daylight length. Seasons result from the tilt of the Earth's axis relative to its orbit around the Sun, which causes changes in solar radiation received at a given latitude.

Two systems are commonly used to define them. The astronomical system assigns seasons to solar positions: spring begins at the vernal equinox, summer at the solstice, autumn at the autumnal equinox, and winter at the solstice. The meteorological system groups seasons by calendar months: spring (March–May in the Northern Hemisphere), summer (June–August), autumn (September–November), winter (December–February). The Southern Hemisphere has opposite months. In practice, the two systems usually align closely but can differ by a day or two.

In the Northern Hemisphere, spring brings warming and increasing daylight, summer is usually the warmest season with long days, autumn brings cooling and shorter days, and winter features cold temperatures and the shortest days. The Southern Hemisphere experiences the opposite sequence.

Seasons influence agriculture, ecosystems, wildlife migrations, and human activities such as clothing, travel, and energy use. In tropical regions, the year is often divided into wet and dry seasons rather than four temperate seasons. In polar regions, daylight varies dramatically, with near-continuous daylight in summer and polar night in winter. Beyond Earth, the concept of seasons depends on axial tilt and orbital dynamics and can differ widely among planets.