Ole Rømer and the Great Discovery

In 2026, the Round Tower marks the 350th anniversary of Ole Rømer’s groundbreaking discovery of the speed of light with an extensive programme. From February and throughout the year, visitors can experience the tower’s historical introductory exhibition, which tells the story of the discovery, the person behind it, and Rømer’s connection to the Round Tower.

350 years ago, the astronomer Ole Rømer made his pivotal discovery that light has a finite speed. But how did he arrive at this conclusion? What does the discovery mean for us today? And who was he beyond this achievement—the man with many talents and a large wig?

Alongside four rotating special exhibitions on light presented over the course of the year, you can experience the Round Tower’s own exhibition on Ole Rømer and gain deeper insight into the man, the discovery, and his relationship to the Round Tower.

Please note that the exhibition cannot be experienced at times when the Library Hall is temporarily closed due to events or during the construction of changing special exhibitions. Check our landing page rundetaarn.dk before your visit, where current closures will be listed at the top of the page.