Deserts are traditionally imagined as unbearably hot places, like the Sahara, but they’re not actually defined by their heat—a desert is a region that receives less than 254 mm of precipitation per year. Under this definition, the Sahara isn’t the largest desert in the world—at just over 9 million square kilometres, it’s easily trumped by the desolate 14.2 million square kilometres of—surprise—Antarctica. A place of deadly snowstorms and impassable ice sheets, Antarctica is the coldest and windiest place on Earth, but also the driest, receiving less than 50 mm of rain per year. 98 percent of the continent is covered in ice and snow, so sunlight is reflected rather than absorbed. The average temperature is -50 degrees Celsius and it is often too cold for any kind of precipitation—cold air can’t hold as much moisture as warm air. However, moisture in the atmosphere is what interferes with the light of stars and planets, causing them to twinkle, so in the dry, high-altitude Antarctic air, the sky is crystal clear—perfect for astronomy.