Mysterious stone circle may be world's oldest observatory

Researchers suspect the ancient stone circle of Nabta Playa was used to determine the summer solstice, signaling the coming rainy season.

The Nabta Playa stone circle dates back 7,500 years. (Photo: Mike P Shepherd).

Nabta Playa, located in the Egyptian desert, may be the world's oldest astronomical observatory. The desert, located in southern Egypt, about 175 miles southwest of Aswan, was once home to the ancient Nubian people. The stone circle was built about 7,500 years ago, making it 2,000 years older than Stonehenge, according to Live Science .

Today, the main pillars of the structure are in a museum in Aswan to prevent vandalism. But originally, Nabta Playa consisted of dozens of upright stones, each more than a meter tall, in the desert 100 kilometers west of the Nile. In addition to the pile above the central tomb, many of the stones appear to have been deliberately arranged in a circle, corresponding to the positions of certain stars. The six stones inside the circle may have served ritual purposes or marked important astronomical events. These stones were surrounded by 29 pillars, forming a kind of primitive calendar.

Excavations of the central tomb in 2001 found no remains, only the complete skeleton of a cow. Along with other evidence, the discovery suggests that Nabta Playa was built by a Stone Age population that relied on herding cattle between the seasonal lakes. The circular stones may mark the rising of the Sun on the summer solstice, signaling rains that would help replenish the lake. The three central stones represent Orion's belt, and several of the stones mark bright stars such as Arcturus, Sirius, and Alpha Centauri.