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.
Autumn: When the Leaves Fall. Autumn begins with the autumnal equinox (September 22, most years). The equinox is the point at which the sun is directly over the equator. From this point throughout the season, the pole is beginning to point away from the sun. The hemisphere is getting more night hours than daylight and this has a cooling effect.