This phenomenon owes its name to an event in 1596 when explorers (in search of the northeast passage) wintering on the island of Nova Zemlya saw a distorted image of the sun two weeks before astronomical calculation would have had it rise. Since that time, the term has been used generically for any such observation of an image of the sun when the actual sun was substantially below the horizon. In the original case, the angular difference between the image and the object was 5°. This is explained by the ducting of the sunlight between the surface and a lifted inversion.