On October 7th, residents of the Chinese cities of Jiangxi and Foshan reported a strange sight - Towering skyscrapers that appeared to be dangling from the clouds. As the video of the 'floating city' went viral, it resulted in various theories. Some speculated the residents had witnessed a window to a parallel universe while others believed they had just stumbled onto a secret NASA project. Then there were the skeptics that dismissed the whole thing as a hoax. While that may still be the case, some experts believe that it could also have been a rare, naturally occurring optical illusion called Fata Morgana.
The 'superior' mirage is caused by the way our eyes see things. As you probably know, vision begins when light rays reflect off objects and enter our eyes. What you may not be aware of is that our brain always assumes that the light waves are being reflected in a straight line.
However, that is not always the case. When light waves cross the boundary between different densities, they diverge. The phenomenon called refraction can be observed by covering one half of a pencil with water. The difference in the density of the water and air causes the light waves that are emanating to deviate from their original path. However, since the brain assumes they are going straight to our eyes, pencil appears bent.
While the same principal applies to the floating skyscrapers, the illusion is rare, especially on land. That's because for Fata Morgana to occur there has to be a temperature inversion. This means the cold dense air layer is below the sparser warm air layer, instead of the other way round.
In the most recent case when light waves from the skyscrapers hit the colder denser layer of air that was closer to the ground, they bent downward. But because of the way our brain is conditioned, the residents saw them as if the light was coming down a straight path. This created the illusion that the buildings were floating.
While that may sound complicated, it is not if you think of Fata Morgana as an inverse (or superior) mirage. In normal (or inferior) illusions the brain creates the illusion that objects are lower than they are. This is the reason desert travelers often mistake the sky for water. In the case of Fata Morgana, objects look higher and hence appear to be elevated. Experts say that the further the observer, the more pronounced the effect.
Though we now know that the eerie but fascinating phenomenon is just an illusion, such was not the case during ancient times. In fact, Fata Morgana gets it name from the enchantress Morgan le Fey of the King Arthur legends who was known to trick sailors into entering her underwater castle with visions of them floating in the air.
However, the most famous Fata Morgana legend is that of the Flying Dutchman, a ghost ship that haunted the Cape of Good Hope. According to the folklore, the dead crew tried to hand off letters to any sailor that crossed the ship's path! We cannot even imagine what the poor seamen went through.
Resources: wired.com, dailymail.co.uk, techinsider.com