The summer solstice occurs on June 21st at 7:28 am EDT. At this moment the center of the Sunâ€™s disc stands directly overhead at a point on the Tropic of Cancer in the southeastern corner of Algeria. A few hours earlier Old Sol stood virtually overhead in the Egyptian city of Aswan, known to the Greek astronomer Eratosthenes in about 240 BCE as Syene. Eratosthenes also knew that on the summer solstice in Alexandria, Egypt the Sun was just over seven degrees from the zenith. Having traveled by camel from Syene to Alexandria, he estimated the distance between the two cities and used geometry to estimate the circumference of the Earth. His result was remarkably close to our modern value if we make certain assumptions about the units that he used. Still, his method proved that the Earth was indeed a sphere of finite dimension. For most of us, the solstice passes more or less unnoticed except as the marker of the longest day of the year. However, many ancient cultures revered the day, as evidenced by Neolithic and Paleoamerican sites throughout the world.
Happy Solstice to all!