Autumn (also known as fall in North American English) is one of the four temperate seasons. Autumn marks the transition from summer into winter, usually in late March (southern hemisphere) or late September (northern hemisphere) when the arrival of night becomes noticeably earlier.

In theory, astronomically, the equinoxes ought to be the middle of the respective seasons, but temperature lag (caused by the thermal latency of the ground and sea) means that seasons appear later than dates calculated from a purely astronomical perspective. The actual lag varies with region, so some cultures regard the autumnal equinox as "mid-autumn" whilst other treat it as the start of autumn (as shown in the above table).

Autumn starts on or around 15 September and ends on about 6 November in solar term.

In Ireland, autumn begins on 1 August and ends 31 October, due to the Irish calendar.

In Australia, autumn begins on 1 March and ends May 31.

Etymology

The word autumn comes from the Old French word autompne (automne in modern French), and was later normalized to the original Latin word autumnus. There are rare examples of its use as early as the 12th century, but it became common by the 16th century.

Before the 16th century, harvest was the term usually used to refer to the season. However as more people gradually moved from working the land to living in towns (especially those who could read and write, the only people whose use of language we now know), the word harvest lost its reference to the time of year and came to refer only to the actual activity of reaping, and fall, as well as autumn, began to replace it as a reference to the season.

The alternative word fall is now mostly a North American English word for the season. It traces its origins to old Germanic languages. The exact derivation is unclear, the Old English fiæll or feallan and the Old Norse fall all being possible candidates. However, these words all have the meaning "to fall from a height" and are clearly derived either from a common root or from each other. The term came to denote the season in the 16th century, a contraction of Middle English expressions like "fall of the leaf" and "fall of the year".

During the 17th century, English immigration to the colonies in North America was at its peak, and the new settlers took their language with them. While the term fall gradually became obsolescent in Britain, it became the more common term in North America, where autumn is nonetheless preferred in scientific and often in literary contexts.

Harvest association

Association with the transition from warm to cold weather, and its related status as the season of the primary harvest, has dominated its themes and popular images. In Western cultures, personifications of autumn are usually pretty, well-fed females adorned with fruits, vegetables and grains and wheat that ripen at this time. Most ancient cultures featured autumnal celebrations of the harvest, often the most important on their calendars. Still extant echoes of these celebrations are found in the mid-autumn Thanksgiving holiday of the United States, and the Jewish Sukkot holiday with its roots as a full moon harvest festival of "tabernacles" (huts wherein the harvest was processed and which later gained religious significance). There are also the many North American Indian festivals tied to harvest of autumnally ripe foods gathered in the wild, the Chinese Mid-Autumn or Moon festival, and many others. The predominant mood of these autumnal celebrations is a gladness for the fruits of the earth mixed with a certain melancholy linked to the imminent arrival of harsh weather.