Timekeeping  /  The shadow clock
c. 1450 BC

The shadow clock

A raised end throws its shadow along a marked bar; summer hours ran longer than winter ones.

The shadow clock
The shadow clock of Thutmose III: a greywacke bar 23 cm long, inscribed with the king’s names. The upright peg at the end is a modern restoration.Photograph: Ägyptisches Museum und Papyrussammlung, Berlin, ÄM 19744 · CC BY-NC-SA 4.0
Morning: the shadow of the upright shortens along the five marks. At noon the clock is turned round for the afternoon.Drawing: Watch Historian
The need
Egyptian temples and officials divided daylight into twelve hours, but those hours changed length with the season. A small portable instrument that read the sun’s shadow gave a working hour without any calculation.
How it worked
The stone is an L: a short upright at one end and a long bar with five marks. Set level and pointed towards the sun, the upright throws a shadow along the bar; as the sun climbs the shadow shortens past the marks, one for each hour. At noon the instrument is turned to face the other way for the afternoon.
What it changed
This is the oldest surviving instrument for telling the time of day. A text carved in the cenotaph of Seti I at Abydos, about 1290 BC, explains how such a clock was made and used, the only ancient instruction text for an Egyptian sundial.
Where it is now
Ägyptisches Museum und Papyrussammlung, Berlin. Bought by Ludwig Borchardt from a dealer in Cairo; said to come from Hermopolis.

SourcesÄgyptisches Museum Berlin, ÄM 19744 · McMaster AEA, SL Berlin ÄM 19744 · Salmas, “La mesure du temps de la journée”, BIFAO 113 (2014)

Suggest a correction

Spotted an error, or know a better source? Tell us. Notes go to the editor and are not published.