sun + dial

Sundial is a compound of 'sun' and 'dial' (from Latin dialis, daily, from dies, day). The word appeared in English in the 1500s, though the device is far older. Egyptian shadow clocks date to at least 1500 BCE. The obelisks of Egypt were, among other things, enormous sundials — the shadow of the obelisk moved across the ground, marking the progression of the day.

The Greek gnomon — a vertical stick that casts a shadow — was the simplest sundial. The word gnomon means 'one who knows' or 'indicator.' Anaximander of Miletus is traditionally credited with introducing the gnomon to Greece from Babylon in the sixth century BCE. The Romans built elaborate stone sundials with hour lines and Latin inscriptions — many survive. The sundial was the primary timekeeping device for the entire classical world.

Sundials have an inherent limitation: they only work when the sun is shining. Cloudy days, nighttime, and indoor spaces defeated them. The water clock (clepsydra), the hourglass, and eventually the mechanical clock were all invented to keep time when the sundial could not. But until the seventeenth century, clocks were set by sundials — the shadow was the reference, and the machine was the approximation.

Sundials now appear primarily in gardens as ornamental objects. They carry inscriptions that lean toward melancholy: 'I count only the sunny hours.' 'Tempus fugit.' 'Grow old along with me.' The sundial became a memento mori — a reminder of time passing. The device that once did practical work now does philosophical work.