hemispherical sundial

A hemispherical sundial, or hemicycle, is a type of timekeeping device attributed to the Greek astronomer Aristarchus of Samos around 280 BCE. This instrument featured a hemispherical opening cut into a block, with a pointer fixed at the center. The tip of the pointer's shadow traced an arc across the internal surface of the hemisphere, which was marked with divisions to indicate the time.1

These divisions represented seasonal hours, meaning their length varied with the seasons because the length of the day changes. This design was widely used for centuries. A variant, invented by Berosus, involved cutting away part of the spherical surface south of the longest day's shadow arc. The Greeks and Romans further developed sundials, often incorporating geometrical complexity and using seasonal hours.1