If the sight of a ship apparently hovering over the sea is a very rare event in the UK, then every two days should be an even more unlikely occurrence.
But 13 days after a giant tanker was photographed floating above the water off Cornwall, the effect of an optical illusion known as the upper mirage, similar images emerged from the cruise ship, the Jewel of the Seas, off the coast of Dorset.
When the Cornwall illusion occurred, BBC meteorologist David Braine said it was common in the Arctic, but can appear “very rarely” in the UK during the winter.
It is caused by a meteorological phenomenon called temperature inversion. Normally, the air temperature drops with increasing altitude, making the top of the mountains colder than the foothills. But in a temperature inversion, the hot air is on top of a colder air strip, wreaking havoc on our visual perception. The occurrences in Cornwall and Bournemouth were caused by the cold air over the relatively cold sea, with the warmer air above.
The coronavirus pandemic caused cruise ships that would normally be in distant locations to be anchored off the English coast.
Bournemouth Echo published photos taken on Wednesday night of Jewel of the Seas and Anthem of the Seas, many of which were shared on the camera club’s Facebook page.
David Morris said he was “surprised” when, on March 4, he noticed a giant tanker floating on water while looking out to sea from a village near Falmouth, Cornwall, and took a picture for posterity.
Superior mirages have long allowed photographers around the world to obtain stunning images of ships, yachts and other vessels apparently hovering in the air. A potential clue that the view is a mirage is the lack of any detail below the vessel’s waterline: for example, a mirage of a “hovering” yacht without the bottom hull and keel.
More common optical illusions are the “lower mirages” that give rise to apparent oases in the desert and puddles on hot summer roads, caused by the colder air over a layer of hot air, directly above a road, for example. When sunlight coming down from the sky approaches the air near the hot surface, it is curved upwards towards the eye of the observer, making the sky appear to be reflected in the road.