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 starts Tuesday, according to meteorologists. Meteorological fall (aka autumn) is defined as the months of September, October and November in the Northern Hemisphere (it's spring in the Southern Hemisphere). Most people consider the first day of autumn to be the autumnal equinox, which this year is September 23, according to WeatherBug meteorologist Mark Hoekzema. This is because, astronomically, the sun will be directly overhead of the equator as the Earth`s tilt begins to point the Northern Hemisphere away from the sun.