The Pantheon a sundial?

Friday, February 20th, 2009

By Caroline Prosser/The Roman Forum
February 2009

Scientists believe the Pantheon may have acted as a colossal ancient timekeeping device after an expert observed changes in the paths of light beaming through the empty space, or oculus, in its domed ceiling.
Scholar Robert Hannah of the University of Otago in Dunedin, New Zealand made the discovery while visiting the Pantheon in 2005, while researching for a book on time in antiquity. According to a report in the New Scientist, he observed that during the six months of winter, the light of the noon sun traces a path across the inside of the roof. During summer however, with the sun higher in the sky, the shaft shines onto the lower walls and floor. At the two equinoxes, in March and September, the light hits the junction between the roof and wall, above the Pantheon’s principal northern doorway, where a panel allows a sliver of light through to the shadowed front courtyard - the only moment in the year that it normally sees sunlight if the main doors are closed.
Hannah says that the Pantheon’s perfectly hemispherical form is a “deliberate design feature” , since a hollowed-out hemisphere with a hole in the top was a type of sundial used in Roman times, on a much smaller scale, to show the time of year. There are no markings because, according to Hannah, sundials were “part of the culture, they wouldn’t need to explain themselves.”
He also says that by marking the equinoxes, the Pantheon was intended to elevate emperors who worshipped there into the realm of the gods. At equinox, the sun is on the celestial equator - where Earth’s equator would lie if projected into space. This was seen by astronomers as the most stable part of the sky, a perfect eternal home for the gods. The Pantheon’s very name also means “all of the gods”.

Historian of astronomy, James Evans, from the University of Puget Sound in Washington state was intrigued by the findings : “The architect of the Pantheon would certainly have been aware of the symbolic connections between the cosmos and the empire, and between the sun and the emperor.”
The Pantheon was constructed in 27-25 BC and completed and restored by Hadrian in AD 128. It contains the tombs of Raphael and of several Italian Kings.