Jens Olsen's World Clock

Jens Olsen's World Clock or Verdensur is an advanced astronomical clock which is displayed in Copenhagen City Hall.^[1][2]

The clock was designed and calculated by Jens Olsen (1872–1945), who was a skilled locksmith, and later learned the trade of clockmaking. He also took part in the beginning of the clock's construction, and died in 1945, 10 years before the clock was completed.^[3]

The clock consists of 12 movements which together have 15,448 parts.^[4][5] The clock is mechanical and must be wound once a week.^[6] Displays include lunar and solar eclipses, positions of the stellar bodies, and a perpetual calendar, in addition to the time.^[1] The fastest gear completes a revolution every ten seconds and the slowest every 25,753 years.^[1][5]

The calculations for the clock were made up until 1928, after which they were supervised by the astronomer Elis Strömgren.^[5] The drawings for the clock were made between 1934 and 1936,^[7] and the actual production of the clock took place from 1943 until 1955.^[8] The clock was started on 15 December 1955 by King Frederik IX and Jens Olsen's youngest grandchild Birgit.^[1][7]

The clock movements are modular, such that an observer may more easily identify them and understand the functioning of the clock more readily. Information is passed between movements through three means, depending on the type:

1. Rotational information is transmitted via sets of bevels gears at both the source and destination module, with a shaft between them. These are continuously rotating (unbounded), although not always constant speeds. The gearing at both modules is always configured such that the shaft rotates at a meaningful rate (such as 1 rotation per mean day). Note that this is not the simplest design but helps observers understand more readily, likely by intent.
2. Linear translations are transmitted via steel ribbons. These are analog signals of limited range (bounded), such as the current value of the Equation of Time or various solar and lunar anomalies. The ribbons generally go upwards to the top of the case, where there is a bell-crank system to transfer them horizontally to above the relevant destination movement, from which they can descend.
3. Impulses are transferred via rods. These are discretely occurring signals that trigger discontinuous events, such as midnight causing the date to change. These also use the bell-crank system in the top of the case

• Clock of the Long Now
• Rasmus Sørnes

• Otto Mortensen Jens Olsen's Clock: A Technical Description Technological Institute, Copenhagen, 1957.

• The Story of the Astronomical Clock
• Description of Jens Olsen's World Clock Archive.org (Danish)

55°40′32″N 12°34′10″E / 55.67556°N 12.56944°E / 55.67556; 12.56944