The refraction of sunlight usually makes the sun appear flatter or more oval on the horizon during sunsets. This sunset over the Pacific Ocean, photographed by the European Southern Observatory in Chile, is a more pronounced version of that visual effect.
Refraction severely flattens the top of the sun, but its light is brighter because of a shorter trip through the atmosphere. The double sun seen below is called an inferior mirage. This is the most common type of mirage, the one we see all the time on highways on hot days.