Astronomical Clocks of the Middle Ages

A Guided Tour (Part 2)

In Part 2 we look at some extant examples of medieval astronomical clocks, from all over Europe. We include links to web-sites with photos and further information about these clocks.

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Stage 0: No Dial

One of the oldest surviving mechanical clocks in the world is the one in Salisbury Cathedral, made in about 1386. The clock has no dial, its sole function is to strike the hours.

Stage 1: Moving dial

A few clocks with moving dials survive in museums.

Stage 2: Sun-Clock

This stage is purely theoretical: no examples known to the author!

Stage 3: Sun-Moon

Here we're on safer ground. There are several examples of sun-moon clocks in the West of England:

• a famous one in Wells Cathedral (click here for a picture). Dates from the second half of the 14th century.
• a somewhat less elaborate example at Exeter Cathedral, dating from 1423 (click here for a picture).
• still humbler examples at the parish church of Ottery St. Mary (Devon) (picture) and at Wimbourne Minster (Dorset)(picture).

Stage 4: Sun-Moon-Zodiac

• Padua One of the earliest public clocks of this type was built by Jacopo de Dondi (father of Giovanni de Dondi of Astrarium fame) at Padua in 1344. Unfortunately this clock was destroyed in fighting between Padua and Milan in 1390. However it was replaced in 1423 by the present, magnificent clock (believed to be similar to the original one). Click here for a picture (J.Podosky's site; see Prague below). The purpose of the geometric figures at the centre is to enable one to tell at a glance whether the moon is making a significant astrological aspect to the sun (e.g. 90 degrees, 120 degrees etc.).
• Venice The famous clock in St. Mark's Square, housed in the Torre del' Orologio, completed 1499. The clock was recently restored by the Swiss firm Piaget. For a good photo of the clock-face have a look at this on-line article about the clock (scroll down to the 4th picture, and click on it). It is believed that at the centre of the clock-face there were once concentric rings carrying emblems of the planets, showing the mean motion of the planets about the earth. Alternatively, there may have been more elaborate dials (similar to those on de Dondi's Astrarium), showing the true positions of the planets as they appear to us. Note the first hour beginning at what we would call the 3 o'clock position: a relic of the old Italian system of reckoning 24 hours from sunset to sunset.
• Hampton Court Palace (1540) - click here for a picture. The palace built by Cardinal Wolsey and 'given' to Henry VIII in 1528. The clock probably designed by Nicholas Kratzer, the subject of a well-known portrait by Hans Holbein (note the polyhedral sun-dial).

Stage 5: Astrolabe Variant

• Prague. Built 1410, at the Town Hall. Believed to be essentially unaltered (including the clock mechanism) since it was built. See the excellent picture at J.Podolsky's web-page about the clock (part of the web-site of the Relativity Group at Charles University, Prague).
• Lund Cathedral. The original clock goes back to 1380, but it was restored in the 1920's. Find it in this virtual tour of the interior of the cathedral.
• Berne - the Zytgloggeturm (clock tower); dates from 1530.

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