Theinvention of the sundial merges with the history of two ancient civilizations, Egypt and Mesopotamia. Later adopted by the Romans and Greeks, this tool was of great use for administrative and especially religious organizations, the latter often punctuating daily activities. Today there are still many sundials from these eras, in various forms: spherical, concave, convex, hemispherical ...
It was the Greek historian Herodotus (c. 484-c. 420 BC) who was the first to mention the ancestor of the sundial, called gnomon, invented by the Babylonians. We can put forward the idea that the gnomon was used long before this first mention. The principle is simple: a stick planted in the ground casts its shadow on a plane on which one can determine, following previously established observations, the hours of the day and the periods of the year. The invention is transmitted to the Egyptians who create the true vertical sundial in the 20th century BC At the same time, the Mesopotamians invented the polo shirt where the shadow of style is projected onto a hollow hemisphere.
A sundial is made up of two parts: the gnomon and the plane of the dial. The gnomon is usually made of a metal rod called a style, parallel to the axis of the Earth and pointing towards the celestial pole. The plane of the dial is the surface where the twenty-four meridians, or hour lines, are drawn. A sundial must be adapted to the latitude. Tables are used to calculate universal time from solar time because solar time is irregular, as the apparent speed of the Sun varies throughout the year. Sundials were used before the use of clocks and watches spread, as early as the 18th century.
- 30,000 years of inventions by Thomas Craughwell. Gründ, 2009.
- The 1001 inventions that changed the world of Jack Challoner. Flammarion, 2010.