autumn

Autumn, also called fall in North American English, is one of the temperate seasons, between summer and winter. In the Northern Hemisphere it is characterized by cooling temperatures, shorter days, and a shift from active growth to dormancy. Astronomically, it begins with the autumnal equinox (around September 22–23) and ends at the winter solstice (around December 21). Meteorologically, autumn comprises September, October, and November. In the Southern Hemisphere, autumn runs March through May.

Leaves often change color and fall as chlorophyll is broken down, revealing carotenoids and anthocyanins that yield yellow, orange, and red hues. Deciduous trees shed leaves, and many crops—such as apples, pumpkins, and grapes—are prominent during harvest seasons.

Weather is variable, but autumn generally brings cooler air, more fluctuation between warm days and cool nights, and an increased risk of frost in some regions.

Ecologically, animals prepare for winter: birds migrate to warmer areas, and mammals fatten stores or reduce activity in advance of colder weather.

Culturally, autumn supports harvest traditions and holidays: Canada’s Thanksgiving on the second Monday of October; the United States’ Thanksgiving on the fourth Thursday of November; and Halloween on October 31. The season also inspires foliage tourism and seasonal cuisine.