Everything you need to know: Autumnal equinox of 2011Posted: September 22, 2011
The earliest humans spent more time outside than we do. They used the sky as both clock and calendar. They could easily see that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shift in a regular way throughout the year.
Our ancestors built the first observatories to track the sun’s progress. One example is at Machu Picchu in Peru, where the Intihuatana stone, shown at right, has been shown to be a precise indicator of the date of the two equinoxes and other significant celestial periods. The word Intihuatana, by the way, literally means for tying the sun.