In addition to their vast knowledge of asterisms, wind, waves, and currents, sailors of the Duff and Reef Island groups make use of a unique phenomenon that has barely been documented, let alone witnessed by outside researchers. Te Lapa, literally “the flashing,” was first described as “underwater lightning” by Dr David Lewis in his book We, The Navigators. Chief Kaveia taught his students that these flashes travel on the surface of the ocean, and not underwater. On dark nights, when there is no bright light, as from a full moon, and the sea is not too rough, navigators often see a mysterious light that flashes from islands to a vessel at sea. These flashes come directly from islands beyond the horizon, and show the direction of the islands from the vessel, as when navigational stars are not visible.
The source of these light flashes are not fully understood. This is not typical bioluminescence, but there are some theories and doubters in the the rare scholarly article published, but Te Lapa remains a mystery to those outside of Temotu Province and nearby island groups. It has never been properly photographed (the image above is an artistic rendering). Here’s a PDF containing Dr. Mimi George’s research report in a recent article: