Houston's Iconic Foucault Pendulum Stops Swinging After 50 Years

A historic Foucault pendulum at the Houston Museum of Natural Science has stopped swinging for the first time in nearly 50 years. The device, installed in the 1970s, was designed to demonstrate Earth's rotation with an 81.6 kg weight suspended from the ceiling. Visitors had long watched its slow, steady shift—until a recent technical fault brought it to a halt.

The pendulum was invented in 1851 by French physicist Léon Foucault. Its movement relies on Earth's rotation, causing the plane of oscillation to gradually turn. At Houston's latitude of 29.8° north, the pendulum originally took about 42 hours to complete a full rotation—longer than at most other locations. For comparison, a pendulum in Paris (48.8° north) rotates in 32 hours, while one at the equator would not rotate at all.

The Houston pendulum's motion was maintained by an electromagnetic system at the top. When this system malfunctioned, the pendulum stopped, sparking curiosity among visitors. Museum officials clarified that the issue was purely technical and not a sign of anything unusual. The pendulum's behaviour changes depending on where it is on Earth. At the poles, it would rotate once every 24 hours. Closer to the equator, the rotation slows. This variation helps illustrate both Earth's spin and its spherical shape.

The pendulum's stoppage has highlighted its role as both a scientific instrument and a public exhibit. Once repaired, it will continue its slow, steady turn, completing a full rotation every 48 hours. The museum plans to restore the device, ensuring visitors can again observe Earth's rotation in action.