Summer

Summer returns to the northern hemisphere tonight. It’s the summer solstice — when the Sun stands farthest north in the sky for the entire year. The solstice also brings the year’s longest days.

In centuries long past, the skywatchers of many cultures observed the solstice from special observatories. Some of those observatories were circles of stones. The most famous is Stonehenge in England, but circles of smaller stones were also found in the Americas.

Nabta, EgyptOne of the most ancient stone observatories was built in southern Egypt, at a site called Nabta. It was used at least 6,000 years ago, and perhaps a good bit earlier — many centuries before Stonehenge.

Anthropologists discovered the site almost 40 years ago. Later studies confirmed that Nabta probably served an astronomical purpose.

Among other artifacts, the site contains a 12-foot-wide circle of small stones. Two pairs of stones stand across the circle from each other. Looking through the spaces between each pair reve