The central avenue of Stonehenge points to the northernmost rising of the sun. At the summer solstice, observers can see the rising sun skim a large outlying marker known as the Heel Stone, framed by the monument's ancient pillars.
Ivars Peterson is a freelance writer and editor. He was Director of Publications at the Mathematical Association of America from 2007 to 2014. As an award-winning mathematics writer, he previously worked at Science News for more than 25 years and served as editor of Science News Online and Science News for Kids. His books include The Mathematical Tourist, Islands of Truth, Newton's Clock, and Fragments of Infinity: A Kaleidoscope of Math and Art.