Astronomy Picture of the Day

Explanation: Dominating the top third of Africa is the largest band of dry land on Earth: the Sahara Desert. Stretching across the Sahara are vast plains of sand and gravel, seas of sand dunes, and barren rocky mountains. Only 10,000 years ago, however, grasses covered the region, then rich in mammals such as lions and elephants. Now only two percent of the Sahara are oases, patches of land where crops will grow and where nearly two million people live. Oases are usually centered on natural water springs. Pictured above is colorful and rocky land spanning about 50 kilometers near the Terkezi Oasis in Chad.