In its day, it was one of the most accurate solar observatories in the whole world
Maybe you’ve once stepped into an old European cathedral, and wondered what those zodiac signs were doing there. Isn’t that supposed to be sheer superstition? How did these signs get into a church? Are they simply part of the decoration, a weird Renaissance-Baroque extravaganza, a pagan reference to pre-Christian times, or are they there for another, not-so-well-known reason? Well, actually, they were indeed science, back in the day, although not for astrological reasons –- that is, they had nothing to do with horoscopes or any other so-called “divination” practice — but, instead, for astronomical ones, which are way different from the former. The signs of the zodiac were useful as part of a most accurate instrument, made for measuring solstices. One of the most accurate ones of the day was built in the Basilica of Saint Petronio, in Bologna, which is not only a cathedral but also a solar observatory.
In the cathedral, as the sun reaches its zenith, one can see, through a small hole in the roof of the church decorated with a halo and golden rays mimicking both divine and natural light, a beam of sunlight “touching” a brass and copper line on the floor of the church that runs through more than half the total length of the whole building. Where the line ends, one finds then this constellation of zodiac signs, roman numerals and references to solstices, calendars and other elements of astronomical science. This is what is called a “meridian line,” an element that, surprisingly to many, is just another piece to add to the fascinating puzzle that we might consider religious art is. It is the incorporation of astronomical elements into religious architecture –- that is, yet another instance in which we can find science and faith working alongside one another, following the liturgical calendar.