**The sundial from the Valley of the Kings (front facing).** University of Basel / Kings’ Valley Project / Matjaz Kacicnik

Only count your sunny hours …

"Let others tell of storms and showers, I’ll only count your sunny hours" is a phrase that has graced countless poetry albums. Researchers from the University of Basel have now found out that the sundial has been in use for at least 3,200 years.

Thomas Weibel

Thomas Weibel is a journalist and Professor of Media Engineering at the Fachhochschule Graubünden and the Hochschule der Künste in Berne.

On 19 February 2013, an excavation team from the University of Basel uncovered a limestone fragment in Egypt’s Valley of the Kings with a sundial painted on the front. There is a drilled hole at the top for the shadow-caster, a wooden or metal rod. The timepiece was made by workers engaged in painting the nearby graves of high-ranking persons. It dates from the time of the Pharaohs Amenmesse, Seti II and his wife Tausret, circa 1200 BCE, making it among the oldest in human history. The semi-circular design on the flat, 15.5 by 17.5 centimetre stone, for which the technical term is ‘ostracon’, is divided into twelve parts representing the daylight hours. The hour lines, marked in smooth brush strokes without the aid of a goniometer or ruler, are amazingly even. The two horizontal perimeter lines at the top represent six in the morning and six in the evening; the midday line is drawn vertically from top to bottom. The sundial was portable and would have had to be mounted or placed on a south-facing surface to show the right time – it was actually found near a cliff facing to the south.

**Sundial from the Valley of the Kings (from the back).** University of Basel / Kings’ Valley Project / Matjaz Kacicnik

Shorter and longer hours

At first glance, a vertical sundial looks straightforward. The sun casts a shadow on its east-west trajectory that moves counter-clockwise over the dial face. The hour lines show the time. This is where it gets complicated. In ancient Egypt, the time was divided into twelve equal parts from dawn to dusk. However, because the days are shorter in winter than in summer, a pharaonic hour could last anywhere between 51 and 69 minutes depending on the season. That’s why they are referred to as ‘temporal hours’ – as opposed to the hours we have today based on the mechanical clock and its division of a day into 24 units of equal duration. As temporal and modern hours are only identical twice per year (on the equinoxes, i.e. between 19 and 21 March in the spring and between 22 and 24 September in the autumn), the latter are also known as ‘equinoctial hours’. The shadow caster (gnomon) of the sundial from the Valley of the Kings is no longer in place. Nonetheless, there is an opening for it drilled vertically into the stone, meaning the gnomon was at a right angle to the dial face. This type of sundial is known as ‘canonical’ as it was used as a rough guide for the prayer times in medieval monasteries. However, there is an issue with these canonical sundials: the angle of the sun’s shadow at any given time depends on the season. In the Valley of the Kings, the difference between the equinoxes (21 June and 21 December) was a good five degrees at nine in the morning. To deliver reliable readings throughout the year, canonical sundials need more dials for all the months or star signs, making them not easy to read.

**Sundial in St. Georgen monastery at Stein am Rhein. The sundial showed the prayer times in medieval monasteries.** Wikimedia

Moroccan astronomer and mathematician Abu Ali al-Hasan al-Marrakushi devised a practical solution in the thirteenth century in his work “Collection of the Principles and Objectives in the Science of Timekeeping”: if you don’t attach the gnomon at a right angle to the sundial display, but instead at a latitudinal tilt, making it parallel to the earth’s axis, it casts a consistent shadow at the same time, year in, year out. This gnomon is known as a ‘polar wand’, because it points in the direction of the north celestial pole close to where the North Star (Polaris) is located. Most vertical sundials today have polar wands, which in Switzerland are at a latitudinal tilt of between 45.83 (Chiasso) and 47.56 degrees (Basel).

**Polar wand sundial on the façade of Basel Minster.** Wikimedia

“Sundial country” Switzerland

The pharaonic painters cannot claim astronomical accuracy. Nonetheless, the sundial dating back thousands of years tells us two interesting things. Firstly, it must have been attached to a rockface so it could be seen by everyone from workers to supervisors. That means workers in ancient Egypt must have had certain rights, as an exploitative regime would not have wanted to be so open about working hours. Furthermore, at 11am and midday, and at 2pm, the lines match our current times amazingly well throughout the year. That could indicate a work break at a time of day when the temperatures in the Valley of the Kings were too high and the workers sought the shade of the nearby huts. The limestone relic from the Valley of the Kings may therefore be one of the first examples of a modern method of regulating working hours. 3,200 years later, the sundial constructed in autumn 2011 on Muottas Muragl in the commune of Samedan is centred on accuracy. Thanks to its finely adjustable gnomon, the “most accurate sundial in the world”, in the words of its maker Fred Bangerter, bearing the Latin name ‘Sine sole sileo’ (“without sun, I am silent”), displays the time to an accuracy of ten seconds – albeit only from 21 March to 23 September. During the winter half-year, the sun is too low to activate the high-precision sundial.

**High-precision sundial at Muottas Muragl in Samedan, Graubünden.** Photo: Engadin St. Moritz Tourist Board

More of: Classical antiquity Technology Article Archaeology

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