A Viking ship is late in its return home from the newly discovered lands far west. Winter is around the corner and the weather will soon turn ugly. It's imperative that the helmsman maintains the course due East. But where exactly is Home? The sky is becoming more cloudy every passing day. Most nights the stars are not visible and even during the day the sun has difficulty breaking through. Daylight is short and during good part the sun illuminates the sky from below the horizon . . . somewhere. Hanging from the top of the knorrship mast a sailor squints his eyes looking for clues in the brightness of the clouds . . . to no avail. Then Leif the Lucky spots an opening in the clouds. He reaches for the pouch hanging from his waist and takes out his Sunstone. Through the crystal he looks at the small patch of blue sky. He turns the rock until it becomes yellow. Next he shouts to the helmsman with his stretched arm pointing starboard . . . towards Home. Bees do it. Ants do it. Did the Vikings do it? Can it be that the Vikings used the polarization of skylight as a navigation compass? Did the Vikings find their way to America by looking at the sky through a crystal, the proverbial sunstone? The Icelandic sagas tell the story of how the Vikings sailed from Bergen on the coast of Norway to Iceland, continuing to Greenland and, likely, Newfoundland in the American continent. This remarkable sailing achievement was realized circa 700 -1100 AC, before the magnetic compass reached Europe from China (it wouldn't have helped much, anyway, so close to the Magnetic Pole). How did they steer true course in the long voyages out of land sight, especially in the common bad weather and low visibility of those high latitudes? In 1967, a Danish archaeologist, Thorkild Ramskou, suggested that the Vikings might have used the polarization of the skylight for orientation when clouds hid the sun position. They would have used as polarizers natural crystals available to them, the famous sunstones described in the sagas. To find the location of the sun they only needed a clear patch of sky close to the zenith to determine the great circle passing through the sun. The pros and the cons of this theory are the following.