Strasbourg Astronomical Clock

Pause here for a moment and listen. Under the murmur of voices there is a steady ticking. Coloured light from the windows falls across the floor in patches of red and blue. The stone around you is pink sandstone from the Vosges mountains, and it looks warm even in the cool air of the cathedral. You are standing in the south transept, the arm of the church that crosses the main hall on its southern side. In front of you rises one of the most ambitious machines people have ever built to measure time.

This is the Strasbourg astronomical clock. Look at it slowly, from the floor to the very top. The tall case is painted, carved and crowded with figures. There are dials, a globe, small statues, and a gilded rooster near the summit. At first it can look like a grand piece of church furniture. But almost everything you see is linked by gears to one mechanism. It does more than tell the hour. It follows the sun, the moon, the planets and the calendar of the Church.

The clock in front of you is the third astronomical clock in this cathedral. The first was built in the fourteenth century, in the 1350s. People called it the Clock of the Three Kings, because figures of the Magi bowed before the Virgin Mary. Almost nothing of it survives. The great exception is its rooster. That bird flapped its wings and crowed. It is preserved today in a museum in Strasbourg. It is often described as one of the oldest surviving automatons in the world. An automaton is a machine built to move on its own, like a living figure.

The second clock came in the sixteenth century, during the Renaissance. A mathematician named Conrad Dasypodius designed its astronomy. Two clockmaker brothers, Isaac and Josias Habrecht, built the mechanism. The painter Tobias Stimmer decorated the case. The clock was completed in the 1570s, and visitors came from far away to see it. Here is the first surprise. Much of the case you see today comes from that Renaissance clock. So the outside is far older than the machine inside. You are looking at a sixteenth century cabinet that holds a nineteenth century heart.

Stimmer's paintings deserve a close look. Among them is a portrait of Nicolaus Copernicus, the Polish astronomer who argued that the earth moves around the sun. It is a bold choice for a cathedral in that century, when his ideas were still new and widely disputed. Around the case you will also find religious scenes and allegorical figures, painted in strong reds, greens and gold. The colours have darkened with age, but the detail is still sharp. Take a moment to let your eyes move from panel to panel.

The Renaissance mechanism ran for about two centuries. Then it began to fail, and by the late eighteenth century it had stopped. For decades the painted case stood here in silence. Then a clockmaker from this region, Jean-Baptiste Schwilgué, took on the task. A popular story says he was fascinated by the broken clock as a boy and promised himself he would make it run again. Whether or not the tale is exact, he spent years on calculations. He built the new mechanism between 1838 and 1842.

Schwilgué did not simply repair the old works. He designed a new machine that could do things the old one never could. One of its key parts is the computus. This is the calculation the Church uses to find the date of Easter, a feast that moves each year with the moon. Schwilgué turned that calculation into gears. Around midnight on New Year's Eve, the clock works out the movable feasts for the coming year by itself. Historians of clockmaking often praise this mechanical computus as a landmark in precision engineering.

Now find the dials. Low on the case, a large ring shows the calendar, with the days of the year and many feast days. A figure points to today's date. Higher up, a dial shows the planets from Mercury to Saturn, the ones visible to the naked eye. They circle the sun at their correct relative speeds. Another dial follows the phases of the moon. In front of the clock stands a celestial globe that shows the stars of the sky. Every part moves at its own pace, all driven from the same machine.

Here is the second surprise. The earth wobbles very slowly on its axis, like a spinning top that is running down. Because of this, the positions of the stars shift over a cycle of roughly 25,800 years. Astronomers call it the precession of the equinoxes. Schwilgué built this movement into the clock. One of its wheels needs about that long to make a single full turn. In the time you spend standing here, it moves by an amount far too small for any eye to see.

The clock is also a small theatre. Each day of the week has its own chariot, driven by a Roman god. Apollo, the god of the sun, rides for Sunday. Diana, the goddess of the moon, rides for Monday. The chariot changes at midnight. Above, figures of the stages of life strike the quarter hours: a child, a youth, a grown man and an old man. Then the skeleton figure of Death strikes the full hour. Lower down, two small angels keep time as well. One strikes a bell, and the other turns over an hourglass.

The main performance happens at half past twelve. Why half past, and not noon? The clock keeps the local solar time of Strasbourg, which runs roughly half an hour behind the official time on your phone. At that moment, figures of the apostles walk in procession past Christ, who raises his hand to bless them. Then the rooster at the top flaps its wings and crows three times. This recalls the Gospel story of Saint Peter, who denied knowing Jesus three times before the rooster crowed.

If you come for the midday show, the transept fills quickly, so arrive early and expect to stand. Before or after the show, turn to the tall carved column nearby. This is the Pillar of Angels, from the thirteenth century. It shows the four evangelists, angels with trumpets, and Christ as judge at the end of time. It is an older answer to the same question the clock asks. How do we measure time, and what comes at its end? Stand back far enough to see both together.

Before you leave, look again at the face of the clock. The hands are still moving, slowly and patiently, as they have since Schwilgué set them running in the 1840s. Listen once more for the ticking under the voices of the crowd. As you walk back into the nave, notice the light on the pink stone, and how it has shifted since you arrived. The clock has already recorded that change. The sun has moved, and so have you.