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A Danish Locksmith Spent His Life Building a Clock With a Gear That Turns Once Every 25,753 Years

Copenhageners cycle about 1.4 million kilometres every day.

The Earth's circumference is roughly 40,000 km. So a city of about 600,000 people pedals the equivalent of thirty-five laps of the planet, daily, and then does it again tomorrow.

The rest of the numbers follow from that. There are around 675,000 bicycles in Copenhagen and about 120,000 cars — bikes outnumber cars more than five to one. In central Copenhagen there are more bicycles than residents. 62% of Copenhagen residents commute to work or study by bike; 9% drive. One bridge alone, Dronning Louises Bro, carries up to 36,000 cyclists a day, making it among the busiest cycle crossings anywhere.

63% of members of the Danish parliament, which sits in the middle of the city, cycle to work.

None of this happened quickly, and that is the point. Copenhagen built at least one mile of cycleway every single year from 1912 to 1969. Between 1975 and 1985 it built five miles a year. In 1970, when the city first started counting, the daily traffic was 351,133 cars against 100,071 bikes. In 2016 the count reversed for the first time: 265,700 bikes, 252,600 cars.

That took forty-six years of adding a little every year.

The clock: which is exactly how this city built its most famous object.

Jens Olsen spent decades designing the Verdensur, the World Clock in Copenhagen City Hall — twelve linked movements, 15,448 individual parts, wound by hand once a week. Its fastest gear turns once every ten seconds. Its slowest completes one revolution every 25,753 years, tracking the wobble of the Earth's axis.

Olsen died in 1945, ten years before it was finished. It was started in 1955 by the King of Denmark and Olsen's granddaughter, and it has been running since.

Copenhagen is a city that is comfortable with things that only make sense if you keep adding to them for a very long time.

When Jens Olsen was eight years old, he read a Danish novel in which a clock was broken. It bothered him. If someone had built it, someone could fix it. He decided he would be that person.

He trained as a locksmith, then as an instrument maker, then as a clockmaker. At twenty-five he travelled to Strasbourg to study the astronomical clock in the cathedral, going back again and again to note down how its functions worked. Then he began calculating one of his own.

Jens Olsen's World Clock — the Verdensur — stands in Copenhagen City Hall. It has twelve movements and 15,448 individual parts. It is entirely mechanical and has to be wound by hand once a week.

It shows Copenhagen time, solar time, the time around the world, sunrise and sunset, sidereal time, a perpetual calendar, the positions of the planets, and the dates of future solar and lunar eclipses.

And then there are the gears.

The fastest completes one revolution every ten seconds. The slowest completes one revolution every 25,753 years. That gear is tracking the precession of the Earth's axis — the slow wobble that moves the position of celestial north over roughly twenty-six millennia. It is turning right now. It has moved about three degrees since it started.

Olsen did not live to see it run. He died in 1945. The clock was finally started in 1955, by the King of Denmark and Olsen's granddaughter. His gravestone reads, more or less: astro-mechanic, world clock maker.

One accidental detail: the planetary dial shows eight planets. Olsen finished his calculations before Pluto was discovered in 1930, so it never made the cut. For seventy-six years the clock was considered slightly wrong. In 2006 the International Astronomical Union reclassified Pluto, and the clock quietly became correct again.

The clock: Copenhagen sits at 55.7° north, which produces one of the widest daylight swings on this list — roughly seventeen and a half hours of light at midsummer, and barely seven in late December.

Which is a fitting place for the Verdensur. Above ground, the city runs on a sun that cannot make up its mind. Inside the City Hall, a gear that will not complete its first full turn until roughly the year 27,700 is going round anyway, one hand-wound week at a time.

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