For David Morris, it was an ordinary stroll last month along the cliffs of England’s southwestern coast: his Terrier, a sunny morning, with ships passing on the horizon.
But one vessel seemed a little out of place. It appeared above the horizon, as if hovering over the sea, suspended in the air.
“I told myself, ‘It must be on water,’” said Mr. Morris, a 52-year-old property developer who lives near the Lizard, the most southerly point in mainland Britain. “My head doesn’t want to understand that, but it must be on water.”
Mr. Morris said he hadn’t expected to cause a stir on social media when he posted a photograph that appeared to show the floating ship on his Facebook account. “It’s just a boat picture,” he said in a telephone interview.
forces light from the sun to bend around the horizon.
Cold air usually sits on top of warm air — the more one climbs, the colder it gets. But on that sunny morning in Cornwall last month, the situation was reversed: Cold air lay above the chilly sea, with warm air on top.
The temperature inversion produced a mirage. The light coming from the ship toward Mr. Morris was refracted, because meteorological conditions formed layers of air that had different temperatures, making light travel through them at a different speed.
The ship appeared higher than it should be, because the human brain —and, as it turns out, cameras — can’t process the effect that different temperatures have on how images are perceived.
blue-and-black dress — or was it gold and white? — did in 2015. At least, not yet.
Mr. Morris said this was also not the first time he had seen what appeared to be a floating ship, although the BBC forecaster David Braine said in a short video that what happened was highly uncommon. “It’s quite unusual to see such an optical illusion in British waters, but it does happen very rarely,” he said.
Superior mirages are more common in the Arctic, where they occur because temperature differences between the sea and the air cause a similar change in air density with greater frequency.
But people may be more used to their opposite: inferior mirages. When a hot surface causes cool air to sit on top of warmer air, rays of light are bent upward, leading the viewer to see a patch of blue sky appear in the desert like a pool of water or a mirage on a road.
In Cornwall, Mr. Morris said he had not paid attention for too long to the levitating ship — the Maribel, which was off the coast of France as of Saturday and is scheduled to reach New York on Tuesday.
Instead, he marveled at the landscape around him as he resumed his walk.
He said, “I told myself, ‘How lucky we are to live in this part of the world.’”
Mike Ives and Shannon Hall contributed reporting.