Vikings navigated oceans with sunstones

Viking seafarers, from the 8th to 11th centuries, likely used sunstones—transparent crystals like Icelandic spar—to navigate the treacherous northern waters. These stones exploited polarized sunlight, which is invisible to the naked eye but detectable through the crystal. By rotating a sunstone, navigators could pinpoint the sun's position even on overcast days, a crucial advantage in foggy regions.