Lining Up

The pyramid of Khufu, the largest of the pyramids of Giza, was built with the help of Thuban, a star in the coils of Draco, the dragon. At the time the pyramid was built, about 4,500 years ago, Thuban served as the North Star, so architects aligned the sides of the pyramid with the star's location in the sky. Thanks to a wobble in Earth's orbit, however, Thuban no longer marks the celestial north pole. It will regain that position in another 21,000 years. [Nina Alden Thune/Wikipedia]