Autumn (also known as fall in North American English) is one of the four temperate seasons. Autumn marks the transition from summer into winter. In the northern hemisphere, the start of autumn is generally considered to be around September, and in the southern hemisphere, its beginning is considered to be around March. There exist, however, different definitions of autumn, some of which are based on the months of the year while others are based on the equinox and solstice.
During autumn, deciduous trees shed their leaves. Leaves change to a yellowish, reddish or brownish hue before falling. Such coloured leaves have come to be colloquially called "fall foliage" in North America. In temperate zones, autumn is the season during which most crops are harvested. It is also the season during which days get shorter and cooler and the nights get longer.
Winter is one of the four seasons of temperate zones. North American calendars go by astronomy and state that winter begins on the winter solstice and ends on the vernal equinox. Calculated meteorologically, it begins and ends earlier (typically at the start of the month with the equinox or solstice) and is the season with the shortest days and the lowest temperatures. Either way, it generally has cold weather and, especially in the higher latitudes or altitudes, snow and ice. The coldest average temperatures of the season are typically experienced in January in the Northern Hemisphere and in July in the Southern Hemisphere.