Why does the Sahara become so cold at night?

Deserts often get extremely hot in the day and sharply cold at night because they lack the heat-retaining effects of water vapor and clouds. In the Sahara, clear skies allow the ground to radiate heat into space very efficiently after sunset. Since there is little humidity, there is less greenhouse trapping of warmth near the surface. Sand also heats and cools quickly, so temperatures can drop rapidly overnight. This is why large deserts can have big day-night temperature swings.