Counting the hours

My #histsci-soul-sisterTM, Rebekah “Becky” Higgitt, wrote a charming post on her H-Word Blog to mark the end of European summer time describing the mad scheme of a certain William Willett to introduce the time change in twenty minute increments over several weeks. This reminded me of a local time phenomenon that I’ve not yet blogged about, Der Große Nürnberger Uhr

The time taken for the earth to rotate once upon its axis or for the sun to appear to circle the earth (its irrelevant how you view it) is a given but how one then chooses to divide up this period into smaller, easier to handle units is purely arbitrary. We owe our twenty-four hour day to the ancient Egyptians. They marked the passing of time in the night by the raising of stars; twelve stars being allotted for any given night, thus dividing the night into twelve units. They being normally decimal in their thinking divided the day into ten units. Allotting one unit for twilight at each junction between day and night brought the total to twenty-four.

The ancient Greek astronomers took over the Egyptian solar calendar and their twenty-four hour day dividing the diurnal revolution into twenty-four equally long, or equinoctial, hours as we do now. However most cultures who adopted the twenty-four system before the early modern period divided the night and day each into twelve units producing hours that varied in length depending on the time of year. This variation got larger the further away from the equator the culture was. In the middle of summer daytime hours were very long and night-time ones very short and vice versa in the middle of winter.

Beginning in the fourteenth century the city state of Nürnberg introduced a system of dividing up the day that is a sort of halfway station between the unequal hours of the middle ages and equinoctial hours, the so called ‘Große Uhr’, in English ‘Large Clock’. In this system the number of hours allotted to the day and night changed approximately every three weeks, the number of daytime hours increasing from midwinter (8) to midsummer (16) and then decreasing from midsummer to midwinter. The number of night-time hours doing the opposite.

Date of change 1st half of year Daylight hours Night-time hours Date of change 2nd half of year

8

16

7 January

9

15

16 November

28 January

10

14

26 October

14 February

11

13

8 October

3 March

12

12

22 September

19 March

13

11

5 September

5 April

14

10

20 August

23 April

15

9

2 August

15 May

16

8

11 June

In 1506 the Nürnberger humanists created one of the most complicated sundials in the whole of Europe on the wall of the St Lorenz church in the city.

Sundial on the St Lorenz Church Nürnberg

Sundial on the St Lorenz Church Nürnberg

This sundial shows the time of day in various different variations of hours including of course the Large Nürnberg Clock

The definition on this picture is not good enough to say which lines are which.

The good citizens of Nürnberg continued to use their own unique way of counting the hours right down to the year 1811.

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3 Comments

Filed under History of Astronomy, History of science, Mediaeval Science, Renaissance Science

3 responses to “Counting the hours

  1. Frederic Metin

    The French Revolution tried to establish a 10 hours day (as well as a 10 months year, and 30 days month), but it was abandoned as well as the French Revolution itself was lost into the Napoleonic Empire. Well, I know it’s far from Renaissance, but the French Revolution units may be directly linked to SImon Stevin’s Disme of 1585.

  2. “The time taken for the earth to rotate once upon its axis or for the sun to appear to circle the earth (its irrelevant how you view it)”

    Just to be pedantic, this isn’t true. As I’m sure our host is aware, the time it takes for the Earth to circle around its axis (sidereal day) is a bit shorter then the time it takes for the sun to appear to have circled around to the same point in the sky (solar day). The error is, not coincidently, about one part in 365 (fourish minutes)

  3. Pingback: Giants’ Shoulders #65: The Wallace Edition | The Renaissance Mathematicus

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