Deserts on Earth exist at 30 degrees latitude because of warm air, calm winds and virtually constant areas of high pressure forming in the atmosphere above. These deserts experience dry and hot conditions year-round and see plenty of sunlight, little wind and very little precipitation. This area of desert lands forms in the areas of latitude 30 degrees north to 30 degrees south of the Equator.
The region containing most deserts on Earth takes several names, including the Tropic of Cancer, Tropic of Capricorn and the horse latitudes. In these regions, the sun follows a high orbital path. It appears directly overhead at 12 p.m. at least once a year, a phenomenon occurring no other place on the planet. Although they exist at the same degrees of latitude, deserts bear different physical and biological features. They attain shapes and climates from surrounding landscapes.
Deserts situated near mountains generally experience less rainfall than deserts exposed in flat, open lands, as mountains absorb precipitation before it reaches deserts. The winds generated in the horse latitudes blow from a westerly direction and lack tremendous force. These winds lack the power for moving clouds across continents, which reduces precipitation in deserts. Although beneficial for desert climates, atmospheric conditions in the horse latitudes pose problems for sailors, whose boats slow to a standstill in the absence of winds.