The Omega Sun, or Etruscan Vase Sun, as Jules Verne called it, is a mirage caused by refraction of the sun as it rises or sets at the sea horizon. Its occurence depends on the temperature difference between air and water, the height of the waves, and the height above sea level from which the sunrise or sunset is being observed.
Although an older website and many links will not connect, one of the best explanations remains:
“This grand show is eternal. It is always sunrise somewhere … Eternal sunrise, eternal sunset, eternal dawn and gloaming, on sea and continents and islands, each in its turn, as the round earth rolls.” John Muir
