The double sun image is an effect of optical refraction, he said, but it's a "pretty darn rare" one, and one not fully explained by science. previous sightings of horizontally-aligned double images of the sun and moon are recorded in a book called "Light and Colour in the Outdoors" (English edition: Springer 1993) by the famous Flemish astronomer Marcel Minnaert, which remains the most complete reference on double suns. Read more