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Autumn

One of Earth's four temperate seasons

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Wildpark, Dülmen , North Rhine-Westphalia , Germany
Original: Dietmar Rabich ( Derivative work: Sting ) · CC BY-SA 4.0

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Date definitions

Some cultures regard the autumnal equinox as "mid-autumn", while others with a longer temperature lag treat the equinox as the start of autumn. In the English-speaking world of high latitude countries, autumn traditionally began with Lammas Day and ended around Halloween, the approximate mid-points between midsummer, the autumnal equinox, and midwinter. Meteorologists (and Australia 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.

In the higher latitude countries in the Northern Hemisphere, autumn traditionally starts with the September equinox (21 to 24 September) and ends with the winter solstice (21 or 22 December). In the United States, Labor Day (the first Monday in September) is often informally treated as the end of summer and start of autumn; certain summer traditions, such as wearing white, may be frowned upon after that date. As daytime and nighttime temperatures decrease, trees change colour and then shed their leaves.

Under the traditional East Asian solar term system, autumn starts on or around 8 August and ends on or about 7 November. In Ireland, the autumn months according to the national meteorological service Met Éireann are September, October, and November. However, according to the Irish Calendar, which is based on ancient Gaelic traditions, autumn lasts throughout the months of August, September, and October, or possibly a few days later, depending on tradition. In the Irish language, September is known as Meán Fómhair ('middle of autumn') and October as Deireadh Fómhair ('end of autumn'). Late Roman Republic scholar Marcus Terentius Varro defined autumn as lasting from the third day before the Ides of Sextilis (11 August) to the fifth day before the Ides of November (9 November).

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