Fall begins Sept. 23. Julian Stratenschulte/AFP/Getty Images

In the northern hemisphere, the season of fall begins with the autumnal equinox, which falls on Wednesday, Sept. 23, 2015. The equinox is defined as when day and night are the same length, approximately 12 hours each.

Fall, also known as autumn, is one of four seasons during the year, occupying the space between summer and winter. In the southern hemisphere, fall occurs during the months of March, April and May.

Signs of fall include cooler weather and the turning of the leaves on deciduous trees from green to varying hues of orange, red, purple and yellow that make fall is a popular time for photography, both professional and personal.

Before the 1600s, the term "harvest" was used to describe fall, as farmers would reap what they had sowed in the spring and prepare for the coming winter. The term fell out of use with urbanization in the 1600s, and the word "fall," which is derived from an Old English term, feallan, took its place, according to

Today, the term fall is primarily used in the United States, while autumn is more common in the United Kingdom.

Some beloved fall, or autumn, traditions in the United States include apple and pumpkin picking, apple-cider brewing and celebrating Halloween Oct. 31. Numerous other cultures and countries hold festivals like Oktoberfest in Bavaria, Germany, the Jewish holiday Sukkot, or the mid-autumn or moon festival in China.