World's largest hot desert. Located in north Africa and covers over 3,500,000 square miles (9,000,000 sq km) or roughly 10% of the continent. Mean temperature over 30 degrees C. Variations may also be huge, from over 50 degrees C during the day, to temperatures below 0 at night in summer.
Fall begins (Northern H.) History. Fall begins in the Northern Hemisphere when the Sun is perpendicular to the equator. This day has equal hours of day and night. The first day of Fall is also called the Autumnal Equinox. In many areas it coincides with harvests. The first day of Fall happens between each year between September 22 and 24.
Fall begins Sept. 23. 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.