8/17/2011 10:27:00 AM
Catholic News Service
Catholic News Service photo
Ancient obelisk catches sun in St. Peter’s Square.
VATICAN CITY — Hidden among the paving stones of St. Peter’s Square there is a simple clock and calendar. All you need is a sunny day.
The 83-foot stone obelisk in the middle of the square acts as a sundial that can accurately indicate midday and the two solstices, thanks to a granite meridian and marble markers embedded in the square.
At noon on Dec. 21, the obelisk’s shadow falls on the marble disk farthest from the obelisk’s base, while at noon on June 21 — the summer solstice — the tip of the shadow will fall just a few yards from the obelisk. In between are five other disks marking when the sun enters into which sign of the zodiac.
A long, thin granite strip running from the obelisk toward the pope’s window and through one of the fountains acts as the meridian: a line that indicates when the sun has reached true or solar noon and is at its highest point in the sky.
The church has always been keenly interested in astronomy to help guide and establish fundamental liturgical days and the times of prayer such as the Angelus, which is recited in the morning, at noon and in the evening. While sunrise and sunset are easy to figure out, sundials could accurately tell midday.
Even when early mechanical clocks were introduced, they were a luxury item for a few and not always accurate, so using the sun to mark true noon was an important backup.
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