The autumnal equinox, the harvest moon, harvest festivals, and ancient astronomers

MARK BENDER, MYSHOT, NATIONAL GEOGRAPHIC SOCIETY/PHOTOThere’s a huge stone carving at the top of this sacred mountain; a sundial of sorts. It’s situated at a northward angle of about 13 degrees, the latitude of Machu Picchu, with its corners facing due north, south, east, and west. It’s called Intihuatana, which translates from the native Quechua language as ‘place to tie up the sun.’ The stone casts a shadow at all times throughout the year, except when the sun reaches its zenith (midday) during an equinox. Then and only then, for a very short time, it casts no shadow, whatsoever.