Egyptian 'star clock' (merkhet), c 600 BC.
© Science Museum / Science & Society Picture Library
This star clock or merkhet was used to measure the time at night. The Egyptians timed the apparently regular movements of the stars acros the sky using an equal interval timer such as a water clock, and this set the basis for the Egyptian time-keeping system. This type of indicator was also the first scientific instrument to combine the function of a surveying device and a transit instrument. This merkhet belonged to an Egyptian priest called Bes, son of Khonsirdis, who was the Observer of Hours at the Temple of Horus in Edfu, Upper Egypt.