The photo above showing a beautiful crimson and gold sunset was taken from Marseille, France on January 12, 2007. In the background (at right center), notice the Canigou Mountain — at the eastern end of the Pyrenees Range, along the border of France and Spain. This mountain is approximately 250 km (150 miles) away! What is shown here is simply the image of the mountain and not the actual mountain itself.
Without considering the effect of atmospheric refraction, these mountains are far too distant to be observed from Marseille. However, on occasion, atmospheric conditions permit objects typically too far away to be easily observed to come into clear view. On this evening, summits in the Pyrenees Mountains higher than about 2,300 m (7,546 ft) can be detected. Most of the distance between Marseille and the Pyrenees Range is over the Mediterranean Sea. When the water is colder than the layers of air above it, a ray of light traveling through the lower atmosphere will be bent or refracted downward — the image of a distant object is thus displaced upward (superior mirage).
Notre Dame de la Garde is at the lower right center of the photograph. The faint vertical streak just above the horizon at left center is Comet McNaught.
This type of mirage may account for some UFO sightings. As the atmospheric conditions change, the mountain would seem to sink back down from where it came. Could it be seen visibly sinking or even accelerating out of view if conditions were right?