Gnomonic, the art responsible for the creation of sundials, owes its name to the gnomon, a Greek term which was used to call the stylus planted perpendicularly to the surface of the dial. The function of the gnomon was to project its shadow on the dial as if it were a hand, indicating the progress of the hours thanks to the apparent motion of the Sun which continuously moves the shadow on the dial.
The history of sundials and gnomons is as long as the history of humans and is lost in the mists of time. One of the best-known solar monuments, but certainly not the first one to be built, is Stonehenge in England, built more than 3,000 years ago. Gnomonic art experienced a significant development in the Middle East to the point that there were sundials widespread in Egypt as early as the 15th century. B.C.
The first sundial installed in Rome was a clock raided in Catania during the First Punic War, which certainly did not indicate the correct time given the latitude distance that separates Rome from Catania.
In 200 BC. Plautus complained about the spread of sundials:
“When I was a boy, my belly was my sundial… This dial told me when it was time for dinner unless there was nothing to eat. Now, although there is enough food, we only eat when the Sun wants.”
In 46 BC. at the behest of Augustus, a large obelisk from Egypt was used as a gnomon for a huge sundial, and two obelisks in Rome are still used today as gnomons for the horizontal sundials of Piazza Montecitorio and Piazza San Pietro.
The time system used on these sundials was called temporal or biblical, given that in the Bible time was marked with an ancient time system, which divided the night into 12 parts and the day into another 12: the first began with the dawn of the sun and the twelfth ended at sunset, both in summer and in winter. Consequently, the days were longer in summer and shorter in winter, and the opposite applied to nights. There was a minimal and negligible difference for the low Middle Eastern latitudes where this time system was born, but it took on greater importance when it was brought to our latitudes, which is why they were also called unequal hours.
Engravings on the facade of Santa Maria Novella. These are sundials with diagrams for the time systems: Babylonian, Italic and astronomical oriented towards the east, while on the side facing south there is a part of a dial with biblical hours.
FROM THE MIDDLE AGES TO THE ASTRONOMICAL TIME SYSTEM
During the Middle Ages, a dark age for the arts, gnomonic survived especially in monasteries thanks to the monks who, along with their rigid rules marked by prayer times, needed sundials suitable for dividing the day into regular intervals and passed down the related astronomical and mathematical principles.
Around 1200, two other time systems appeared, which provided 24 hours of equal duration per day: the Italic time system and the Babylonian system. However, while the Babylonian system placed the end of a day and the beginning of the following one at sunrise, the Italic system, the most widespread in the peninsula, as per biblical tradition, placed the beginning and end of the day at the sunset, both in winter and summer. This time system, which nowadays may seem rather bizarre, made it possible to know how many hours of light there were still available before dark, which was fundamental for that society, which was practically still devoid of artificial light and depended on the natural rhythms of day and night.
The Renaissance brought new interest in gnomonics as well as in all the arts. In 1500 the construction of large camera obscura sundials also served for the reform of the Gregorian calendar in 1582.
In the following centuries, the Italian time system was replaced by the astronomical time system, which divided the day into twenty-four hours, placing the beginning and end of the day at midnight, or 12 hours after the sun’s transit over the meridian. This “new” time system took the name of Spanish time, French time, and ultramontane time, acquiring the name of the foreign powers who, by invading our peninsula, effectively imposed it on the territories subjected to them. In May 1786 the Austrian government ordered the construction of the camera obscura sundial in the Milan cathedral and since 1 December of the same year all public clocks had to be set to the new time.
Engravings on the facade of Santa Maria Novella. These are sundials with diagrams for the time systems: Babylonian, Italic and astronomical oriented towards the west, while on the side facing south there is a part of a dial with biblical hours.
Even today, albeit with some modifications, we use this time system in our everyday lives. The first modification was the introduction of the average time, ie imagining a “virtual” sun that passes over our meridian exactly every 24 hours throughout the year. This correction was introduced to be able to adapt our regular mechanical clocks – which have become more precise and reliable – to the time set by the sun. Actually, in some periods of the year we can see the sun pass over the meridian more than 20 seconds late or early every day: these fluctuations are mainly caused by the elliptical orbit of the earth in its annual revolution around the sun.
The second and last modification made to this time system was the international convention of time zones established in 1884, which was joined by Italy in 1893. Italy, like much of Europe, adopted as its official time zone the first Eastern time zone, based on the average time of the locations on the fifteenth meridian East.
Actually, what we are used to calling solar time (standard time) in winter, as opposed to summer time (daylight savings time), is also a conventional time adopted to favour human activities, including transport and telecommunications, resulting in the possibility for Italian to call someone from Italy in Spain at the same time, while the sun continues to rise, peak at midday and set in Italy more than an hour before Spain.