Sundial

Due to chance observations, ancient people noted that the shadow of a tree trunk would change as the sun moved across the sky. Similarly, when a straight stick is planted vertically in the ground, the shadow of the stick also moves and its length changes throughout the day. When the shadow of the stick is short, ancient people understood that it was close to noon, while a long shadow indicated that the day was starting or nearing its end. By using stones, they marked the positions of this shade. Thus, a rudimentary tool for measuring time took shape over 4,000 years ago, and it was called a “sundial.” The Chaldean astronomer Berossus described the sundial in the 3rd century BCE.

Sundials come in various types and shapes. The simplest form is a straight stick known as a “gnomon.” These gnomons can vary in size, from small to large, like Cleopatra’s Needle which still stands in a park in New York City today. However, gnomons have several drawbacks: throughout the year and at the same hour of the day, the shadow of the gnomon changes in both length and direction. Although people replaced the stick with “obelisks” firmly planted in the ground, all the aforementioned drawbacks still persisted.

To mitigate these disadvantages, ancient people devised “sundials” (cadran solaire). A sundial consists of a horizontal square piece of wood and a diagonal piece of wood that is perpendicular to the horizontal surface. The diagonal piece is aligned parallel to the Earth’s axis, meaning it points toward the North Star. Thanks to this, the shadows no longer change direction, allowing ancient people to obtain specific degrees of measurement. Using sundials is quite simple: when placed in sunlight, if the shadow of the sundial aligns with the 9 o’clock mark, it indicates that it is 9 AM. However, sundials are not precise timekeeping devices and can only be used on sunny days. Sundials must be constructed appropriately for each locality. There was an incident where someone stole a sundial from Egypt and placed it in Greece. In this location, the sundial indicated the wrong time, leaving the thief puzzled.

Sundials have been used since ancient times. The oldest known sundial still in existence, found in Egypt, dates back to the 15th century BCE. Both Egyptians and Greeks favored this type of sundial. By the 19th century, watchmakers even used sundials to tell time. In contrast, the Romans did not pay much attention to this timekeeping device, as they continued to use a gnomon placed in front of the Forum to limit the speeches of orators until 491 CE.