The theory of the sundial

Research on sundials is also part of gnomonics today. Like the first use of the sundial, it probably goes back to the Babylonians. However, its heyday was in Greek and Roman Antiquity.
The term scaphe was coined by astronomer Aristarchus of Samos in the 3rd century B.C. His hemispherical bowl sundial is described by Roman Vitruvius in the ninth of his books on architecture in 30 B.C. It is designed as a mirror image of the visible sphere of the sky.


The scaphe allowed astronomers to calculate that the Earth circles the sun as long as 2000 years ago

Inventor of the scaphe: Aristarchus of Samos

Greek philosopher Aristarchus designed the hemispherical bowl sundial in 250 B.C. The scaphe was highly popular with the Greek. It could be found on many public squares.

His astronomical research led him to the conclusion that the sun was a stationary pole circled by the planets.

About 20 years later, Eratosthenes of Cyrene used the scaphe to determine that the Earth was not flat. He even was able to calculate the circumference of the Earth surprisingly accurately.

Calculations of the circumference of the Earth by Eratosthenes with the help of the scaphe

Eratosthenes observed that the bottom of a deep well was entirely lit up by the sun in the town of Syene (Aswan) on a day where the sun had reached its highest point.
He concluded that the sun had to be vertically in the sky at that moment.

Then he measured the inclination angle of the sun in Alexandria with the scaphe and determined that the angle corresponded to 1/50 of a circumference (7.2 degrees).

Then he was able to calculate the circumference of the Earth, since the distance between Alexandria and Syene was already known. His result: The circumference of the Earth is about 50 times as long as the distance between Alexandria and Syene.

The Earth is not flat.

Eratosthenes von Kyrene, astronomer and mathematician

Development of the sundial

Following the very early sundials that were only a simple stick stuck in the ground to create a relation between time and the shadow cast, the sundial was continually developed further.
The hollow-sphere sundial used for scientific purposes by Aristarchus led to the idea of using a hemispherical bowl. The part of the sphere that was pointing south had no functional use.
Even then, it was possible to calculate the duration of a year relatively accurately.


Great scientific progress happened between the 14th and 15th centuries. The idea of putting the rod casting the shadow in parallel with the earth axis made the time scale easier to read. The gnomon's shadow now always remained at the same length, no matter the season. However, determination of the latitude became all the more important now, since the angle for alignment of the gnomon is based on it.