Church Buildings as Sundials

Many central European churches and cathedrals are set up as giant pinhole cameras - they have a tiny hole in the dome or cupola and an inscribed meridian line somewhere inside. When the sun's projected image crosses the "noon mark", it indicates noon local time.

The most famous such arrangement was designed 350 years ago by the astronomer Gian Domenico Cassini for the Church of San Petronio in Bologna, Italy. The following is a photo of the sun's partially eclipsed image projected on the floor of a church this past August. Franco Martinelli, an Italian astronomer, has this and similar photographs on his web site:

Published in the October 1999 issue of the NightTimes