Autumn, also known as fall in American English and Canadian English, is one of the four temperate seasons. Autumn marks the transition from summer to winter, in September Northern Hemisphere or March Southern Hemisphere, when the duration of daylight becomes noticeably shorter and the temperature cools considerably. One of its main features in temperate climates is the shedding of leaves from deciduous trees.nnSome cultures regard the autumnal equinox as `mid-autumn`, while others with a longer temperature lag treat it as the start of autumn. Meteorologists and most of the temperate countries in the southern hemisphere use a definition based on Gregorian calendar months, with autumn being September, October, and November in the northern hemisphere, and March, April, and May in the southern hemisphere.nnIn North America, autumn traditionally starts on September 21 and ends on December 21. It is considered to start with the September equinox 21 to 24 September and end with the winter solstice 21 or 22 December. Popular culture in the United States associates Labor Day, the first Monday in September, as the end of summer and the start of autumn; certain summer traditions, such as wearing white, are discouraged after that date. As daytime and nighttime temperatures decrease, trees shed their leaves. In traditional East Asian solar term, autumn starts on or around 8 August and ends on or about 7 November.

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