But 13 days after a giant tanker was pictured floating above the water off Cornwall, the effect of an optical illusion known as a superior mirage, similar images emerged of the cruise ship, the Jewel of the Seas, off the Dorset coast.
When the Cornwall illusion occurred, the BBC meteorologist David Braine said it was common in the Arctic but can appear “very rarely” in the UK during winter.
It is caused by a meteorological phenomenon called a temperature inversion. Normally, the air temperature drops with increasing altitude, making mountaintops colder than the foothills. But in a temperature inversion, warm air sits on top of a band of colder air, playing havoc with our visual perception. Both the Cornwall and Bournemouth instances were caused by chilly air lying over the relatively cold sea, with warmer air above.
The coronavirus pandemic has led to cruise ships that would usually be in far-flung locations being anchored off the English coast.
The Bournemouth Echo published pictures taken on Wednesday evening of the Jewel of the Seas and Anthem of the Seas, many of which had been shared on its camera club Facebook page.
David Morris said he was “stunned” when, on 4 March, he noticed a giant tanker floating above the water as he looked out to sea from a hamlet near Falmouth in Cornwall, and took a photograph for posterity.
Superior mirages have long enabled photographers around the world to take striking images of ships, yachts and other vessels apparently hovering in mid-air. One potential clue that the sight is a mirage is the lack of any detail below the vessel’s waterline: for example a mirage of a “hovering” yacht lacked the lower hull and keel.
More run-of-the-mill optical illusions are the “inferior mirages” that give rise to apparent oases in the desert and puddles on hot summer roads, caused by cooler air sitting on 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 bent back upwards to the observer’s eye, making the sky appear to be reflected on the road.