For David Morris, it was a common walk along the cliffs of England’s south-west coast last month: his Terrier, a sunny morning, with ships riding on the horizon.
But one vessel looks slightly out of place. It appeared above here the horizon, as if floating over the sea, hangs in the air.
“I said to myself, ‘It has to be on the water,'” he said. Morris, a 52-year-old real estate developer who lives near the lizard, the southernmost point on the British mainland, said. “My head does not want to understand it, but it must be on the water.”
Mr. Morris said he would not cause a stir on social media when he posted a photo showing the floating ship on his Facebook account. “It’s just a boat photo,” he said in a telephone interview.
But of course it was not. Now many people are trying to turn their heads around a picture that depicts the impossible.
What mr. Morris, according to him, was an example of an optical illusion known as a superior air reflection, which occurs when the temperature difference between the sea and the air causes a change in the air density and the light of the sun down to bend 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 cold sea, with warm air on top.
The temperature inversion produced a mirage. The light coming from the ship in the direction of mr. Morris comes, is broken, because meteorological conditions formed low air that had different temperatures, causing the light to move at a different velocity.
The ship appeared higher than it should have been, because the human brain – and as it turns out, cameras – could not process the effect that different temperatures had on the image’s observation.
(Stay there.)
Light usually moves through straight lines to the eyes, which makes them see in a straight way, dr. Claire Cisowski, a research fellow in optics at the University of Glasgow, said.
But, she said, “sometimes an image is deviated as the rays of light we reach pass through different layers.”
This is what happens when looking through water: A straw in a glass of water or a hand immersed in the sea may not seem in line, because light moves at different speeds through air and water.
The same principle applied to the ship in Cornwall, except that light instead of moving from water to air, moved from air to air, dr. Cisowski said.
“Air is not always the same – it has different properties, whether it is cold or hot,” she said. “So, as light moves differently through these different layers, our brain tries to make sense of it.”
In the case of mr. Morris, as cold air is denser than warm air, rays of light coming from the ship are bent downward. From the coast it has for mr. Morris looked as if the ship was in a higher position than it really was.
“When the light comes into our eyes, they cannot trace the entire path back as if it were bent,” Dr Cisowski said. “So we form an image as if it were coming from a straight line, because our eyes want to lengthen what they see.”
And like an eye, a camera also cannot reconstruct the curved path, according to dr. Cisowski. “It’s as if the ray of light is also coming from a straight line.”
This is not the first time optical illusions on the internet have gone viral, and the floating ship has not achieved the same fame as a blue-and-black dress – or was it gold and white? – done in 2015. At least not yet.
Mr. Morris also said it was not the first time he had seen a floating ship, although BBC forecaster David Braine in a short video that what happened was highly unusual. “It is quite unusual to see such an optical illusion in British waters, but it is very rare,” he said.
Superior air reflection is more common in the Arctic, where it occurs because temperature differences between the sea and the air cause a similar change in air density with greater frequency.
But people are perhaps more accustomed to their opposite: inferior mirage. When a hot surface causes cool air to sit on top of warmer air, rays of light are bent upward, causing the viewer to see a blue sky appear in the desert like a puddle of water or a mirage on a road.
In Cornwall, Mr. Morris said he did not pay attention for too long to the lever – the Maribel, which was off the coast of France from Saturday and would be in New York on Tuesday.
Instead, he marveled at the landscape around him as he began to walk again.
He said, ‘I said to myself,’ How happy we are not to live in this world. ”
Mike Ives and Shannon Hall reported.