Autumn, interchangeably known as fall in North America, is one of the four temperate seasons. Autumn marks the transition from summer into winter, in September (Northern Hemisphere) or March (Southern Hemisphere), when the arrival of night becomes noticeably earlier and the temperature cools considerably. One of its main features is the shedding of leaves from deciduous trees. In North America, autumn is usually considered to start with the September equinox (21 or 22) and end with the winter solstice (21 or 22 December). (Wikipedia)