It sounds like something from a Studio Ghibli movie. Thousands of residents of Jiangxi and Foshan in China reported seeing a floating city appear in the sky. This mysterious city appeared to show skyscrapers towering out of the clouds, and people laid claim that it was all kinds of weirdness.
Some people claimed it was a portal opening up to another dimension, others claimed it was a secret NASA experiment known as "Project Blue Beam" which involves the space agency trying to establish a new world order by staging an alien invasion or the second coming of Christ. Others said it was the Chinese government testing some kind of holographic instrument.
Of course, none of those were correct. Instead meteorologists said it was an optical illusion, a type of mirage known as fata morgana.
These mirages—which can appear on land or sea and have been linked to sailors of the past seeing ghost ships and castles that weren't there—distort distant objects making them appear where they are not, as rays of light get bent when they pass through air layers which have different temperatures.
"The illusion is due to a slightly unusual temperature structure in the lower part of the atmosphere," Prof. Kenneth Bowman, an atmospheric scientist in Texas A&M University's department of geosciences, told The Christian Science Monitor.
"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."
The image below from the Telegraph explains what's happening.
So, not as exciting as a floating city or vortex to another dimension, but the truth is always rather dull.