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.
By NINA RUGGIERO September 22, 2014. In many of our hearts and minds, the start to fall is not scientific. It's the moment the air gets cooler, the moment we slip on our first sweater, the moment we order our first pumpkin spice latte. But fall does not begin in the Northern Hemisphere, officially, until the minute the autumnal equinox strikes. Here's a quick explainer.