The Leaning Tower of Pisa – a Sun Dial?
I am still in Italy, and the sun is shining brightly. The Leaning Tower of Pisa is a freestanding bell tower, of the cathedral of the Italian city of Pisa. It is situated behind the Cathedral and is the third oldest structure in Pisa’s Cathedral Square after the Cathedral and the Baptistry. Now this to me should be a sundial. Am I coo coo or what? Maybe I’ve been thinking too much about my next cuckoo clock article.
Anyways, around 3500 B.C., the Egyptians built obelisks—tall four-sided tapered monuments—and placed them in strategic locations to cast shadows from the sun. Their moving shadows formed a kind of sundial, enabling citizens to partition the day into two parts by indicating noon. They also showed the year’s longest and shortest days when the shadow at noon was the shortest or longest of the year.
Around 1500 B.C., the Egyptians divided the sundial into 10 parts, with two twilight hours indicated. This sundial only kept accurate time (in relative terms) for a half day. So at midday, the device had to be turned 180 degrees to measure the afternoon hours.
A sundial tracks the apparent movement of the sun around the earth’s celestial pole by casting a shadow (or point of light) onto a surface that is marked by hour and minute lines. That is why the shadow-casting object (the gnomon or style) must point towards the north celestial pole, which is very near Polaris, the North Star. The gnomon serves as an axis about which the sun appears to rotate.
The sharper the shadow line is, the greater the accuracy. So, generally speaking, the larger the sundial the greater the accuracy, because the hour line can be divided into smaller portions of time.
I still think this Leaning Tower could be a sun dial.