Åtvidaberg is in southeast Sweden, about 30 miles from the Baltic Sea. It’s a small industrial town, once dominated by copper mining and manufacturing. Today the town is best known for three things: great fishing, fanatical football, and an explosive time keeper—quite literally.
Åtvidaberg’s sun cannon is the only functioning time piece of its kind in the world that still works, and it works every day from the beginning of May through the end of August. The cannon is housed in a small tower on a hill, on the grounds of what used to be extensive estate gardens. When it was built in 1853, these strange cannon-clock devices were common at large estates to help keep track of the time.
It works like this: At midday (or during Daylight Savings Time, 1:00 pm), when the sun reaches its highest point, a lens focuses the sunlight on a small charge of black powder loaded into a 6-pound cannon. Add up some intense sunlight, a little gunpowder, a reasonably sized cannon—and boom! The total is everyone in town knowing it’s time for lunch.
The lens is attached to a movable arm, so it can be adjusted to the sun’s different meridian latitude. But on cloudy days, fear not: the cannon isn’t entirely dependent on solar ignition. On those days the on-duty gunner will manually ignite the charge, so 1:00 never passes in Åtvidaberg unnoticed.