From calendar to the clock

These systems only served to measure certain periods of time and did not consider that days have different durations, depending on the season - and it was not possible to divide or calculate the time in hours, or to measure the elapsed time between the hours. Based on observation of the lunar cycles, the inhabitants of Sumer (in Mesopotamia, present-day Iraq) created the first lunar calendar, some 2,500 years before the Christian era. The year had 12 months of 29 or 30 days - that is, there were days left at the end of each year. It was later enhanced by the Babylonians, another people who lived in the region. The first solar calendar, based on the Earth's movement around the Sun, was a Egyptians' brainchild. It was the first calendar with a 365 days year.

Next came the Julian calendar, instituted in Rome in 46 B.C. Inspired by the Egyptian calendar, it also had a 365 days year, but added one day every four years. Named after Julius Caesar, then consul of Rome, the Julian calendar was used to measure time for approximately 1,500 years. In 1582 it was replaced by the Gregorian calendar, instituted by Pope Gregory XIII, which is still used today in the Western world.

The idea of ​​dividing the day into 12 parts, and then in 24, came from the Babylonians. They also divided the hour in 60 smaller parts, based on their mathematical system - and did it all without calculating time online, as we can do today. But minutes only started to be measured and adopted in practice centuries later, when the first mechanical watches were built in Europe. The idea had been tested in China and in the Middle East, but it was in the 16th century that Galileo Galilei started to research the regularity in the movement of pendulums. Based on these studies, in the following century the Dutchman Christiaan Huygens built the first pendulum clock. It started to be manufactured and had a rapid diffusion.