The Ulm Astronomical Clock

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The Ulm Astronomical Clock

• NHAS meeting, March 23, 2007

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The Ulm Astronomical Clock
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Other Astronomical Clocks

• Prague
• Bern
• Strasbourg
• Lund
• Brescia

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Prague, Czech Rep.
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Bern, Switzerland
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Brescia, Italy
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Digressions

• What about non-astronomical clocks?
• Why do we have clocks anyway?
• Why do we have astronomical clocks and why are
  they all old?

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Non-Astronomical (but complex and public) Clocks

• Munich, Germany

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Public Orreries

• Morehead Planetarium, NC
• Human powered in Armagh, Ireland
• Eise Eisinga Planetarium, Netherlands

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Why do we have clocks anyway?

• Timing is old clocks are new (since 1200)
• Consider the ships bell run by a person
• Bells or horns are better for timing because
  everyone can hear them
  
• Public clocks for time are recent (1600s)
• The astronomical clocks are clearly for display
  rather than for utility

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Cathedrals, Clocks, Stadiums

• Towns compete for resources
• They want to look successful, cohesive and rich
• Completion of a tricky project shows that this
  town is such a place
  
• Countries do the same now consider the Space
  Race

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Why Astronomical Clocks?

• High-risk viewers can check against the Sun and
  Moon so its very tricky all the more
  impressive if it works!
  
• Requires a high level of craft and care
  showcases local skills
  
• Pious and not controversial politically
• High-tech of the time

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How does it work?

• (My guess, as I didnt get to tour the workings)
• Pendulum measures out a time unit (probably one
  second with a 1-meter arm)
  
• Pendulum gates a gear wheel, which thus goes
  around in N seconds
  
• Other gears can do any rational multiple of N.

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The Dials and Hands

• The outermost 12-hour dial shows hours and is
  fixed
  
• The Hand arm shows the legal hour it has a
  triangle at the other end to balance it
  
• The Sun arm shows the local Sun hour it has a
  star to balance it
  
• The Moon arm shows the local Moon hour it also
  has a star for balance

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More Dials and Hands

• The Moon ball is half gold and half black it
  shows the phase of the Moon
  
• The Zodiac dial rotates the Sun and Moon are in
  the correct positions on the Zodiac dial
  
• The Zodiac is bas-relief statues on a grid the
  stars behind it are part of the 24-hour dial
  
• The Calendar ring (offset) is part of the Zodiac
  dial it is an ecliptic projection of the Earths
  equator

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Even more Dials and Hands

• Where the Sun arm crosses the Calendar ring shows
  the current date
  
• The 24-hour dial rotates the Sun arm is
  correctly positioned on it (but not the Hand
  arm!)
  
• The point where the Sun arm crosses the Calendar
  ring shows Sun-set and Sun-rise when it crosses
  the black-white boundary

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And Yet MORE

• The Dragon dial shows the Draconic cycle of the
  Moons nodes on the Zodiac
  
• The head shows the ascending node, the tail the
  descending node
  
• When the Sun and Moon line up with the Dragon,
  there will be an eclipse
  
• Sun and Moon at the same end solar eclipse
• Sun and Moon at opposite ends lunar eclipse

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History

• Details not well documented may have changed
  quite a bit in the first century or two
  
• Repair bills from 1536 exist
• There are lots more repair bills the clock
  seems to have spent most of its time not
  working!
  
• Damaged in WWII, restarted in 1951
• Originally in wrought iron, now mostly brass and
  bronze
  
• Converted from pendulum to quartz in 1952 and to
  radio time in 1978
  
• Adjusted from time to time for precession!

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End Notes

• We are now too high-tech for towns to compete
  with such clocks (a pity)!
  
• Ulm is also the site of the first docmented
  glider flights
  
• Take pictures if you go!