If you suddenly see a city floating in the early morning or evening sky it’s not aliens, Arthurian legends, or a holographic trick, but an atmospheric event known as "Fata Morgana."
Residents and news outlets in the cities of Foshan and Jiangxi in China have reported a floating city appearing in the clouds which has launched a host of theories ranging from dimensional portals and parallel universes to those who claim that NASA is projecting a hologram using something conspiracy theorists have dubbed the Blue Beam Project.
According to atmospheric scientists this is the season for the Fata Morgana optical illusion, which typically takes place as temperatures cool rapidly. In summertime, you might see the illusion of heat haze over a hot road with phantom water shimmering on the surface. The apparition of a city or cliff in the sky is one of autumn’s more common optical illusions in the United States as well as China.
Prof. Kenneth Bowman, an atmospheric scientist in Texas A&M University's department of geosciences, says in an interview that the phenomenon Fata Morgana gets its Italian name from Morgan Le Fay, the sorceress of medieval Arthurian legend. Le Fay was said to have cast an illusion or multiple buildings and cliffs over the Straight of Messina in Italy to lure sailors to their death.
Professor Bowman says this optical illusion is not tied to pollution, global warming, or even vengeful fairies, but a common atmospheric set of conditions.
“The illusion is due to a slightly unusual temperature structure in the lower part of the atmosphere,” says Bowman. “Normally the atmospheric density decreases as you move up away from the surface. It’s the density of the air that determines the refracted index. So that’s what makes it behave somewhat like a lens.”
Therefore, a Fata Morgana “is the result of a big temperature inversion in the atmosphere,” Bowman says. Normally, the air cools the further away you move from the Earth's surface. But with a temperature inversion, the air closest to the Earth's surface is cooler than the air further from the surface.
“You can get inversions when temperatures get cold, the ground can cool off faster than the air that’s up above it. Especially in the fall and winter, you can get these shallow inversions.”
Another way is when the air moves in different directions from different levels, and when a warm air mass moves over cold air.
These temperature inversions bounce light rays in unusual ways.
“We’re moving into winter season here so we’re starting to get cold air from the north and it’s going to get cold here in the Northeast here this week so you can get a large cold air inversion like this,” Bowman says. “But when you get this unusual temperature structure in the atmosphere you can get light rays where light scatters off the surface and goes up into the atmosphere and is refracted back down to the surface again."
“It’s not exactly a reflection because it’s not a mirror but it’s like looking through a lens and you’re seeing the surface at a long distance away but it looks like it’s floating up in the atmosphere," Bowman says.
The Fata Morgan often appears to be shifting rapidly, from a "ship" or "island" right side up, and seconds later, upside down.
“In fact, they’re commonly seen over water,” he says. "Exactly what’s happening in China, I really can’t tell without the weather maps, but it’s more common near large bodies of water, or over water.”
Asked if he thought it was a NASA projection, Bowman says, “No, that falls into the category of wacko.”