Follow the Vikings: A student exercise in optics and navigation inspired by history

It is unclear to historians how Vikings navigated the seas. Centuries before magnetic compasses were introduced to Europe, Viking seafarers traveled long distances to far-flung locations like North America and the Black Sea.

One explanation, although unverified, is known as the “sunstone hypothesis.” This hypothesis suggests that Vikings navigated by using the polarization of the sky to locate the sun, which is often hidden in cloudy northern latitudes. Inspired by this, Karlíková et al. developed a laboratory activity for undergraduate students to recreate polarization-based navigation.

Their activity combines two exercises. In the first, students create a sun compass — which resembles a sundial but rotates to measure cardinal directions rather than time — to determine the direction of true north. Then, by measuring the polarization pattern of the sky with a polarizing filter, they can estimate the location of the sun even when it is obscured.

“Connecting physics to real-life or historically meaningful situations is very valuable. It gives abstract concepts a concrete purpose, and students see that ideas like polarization, solar geometry, uncertainty, and instrumental limits are not just textbook topics,” said author Jan Šlégr. “In this case, the historical framing also opened up a natural conversation about the difference between a fascinating hypothesis and a reproducible result.”

Šlégr says students are more curious and connected with science when testing a historical concept rather than carrying out traditional optics experiments with polarizers and lenses.

“More than specific knowledge of astronomy or polarimetry, I hope students take away the importance of testing attractive theories critically,” he said. “The deeper lesson is that even a beautiful or culturally appealing idea has to survive experimental verification.”

Source: “Viking navigation: From speculative history to laboratory exercise on polarization,” by Kateřina Karlíková, Jonáš Kubeček, Leontýna Šlégrová, and Jan Šlégr, American Journal of Physics (2026). The article can be accessed at https://doi.org/10.1119/5.0295411 .