For the second time in three months, a mysterious "floating city" has appeared in the skies above a Chinese city.

The massive and ephemeral city that suddenly appeared this week in the skies over the city of Yueyang in Hunan province along the southern shores of Dongting Lake caused panic among some residents and was caught on videos later uploaded online.

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One of the videos can be viewed here.

The videos triggered an expected response from UFO true believers in China and abroad, who said the floating city was a gigantic alien mothership that revealed itself for some reason or other.

In October 2016, another "floating city" was viewed hovering in the sky above the city of Foshan in Guangdong province. Foshan lies on the Fen River in the estuaries making up the west side of the Pearl River Delta.

A well known UFO hunter emphasized the apparition was really an alien mothership and that aliens seemed to be very interested in China for some strange reason.

"I believe that this is a UFO mothership that is using the China smog problem for its own benefit so that it can make a rare appearance by flying low and doing some serious research on the humans in Yueyang city," said Scott Waring.

Well, scientists who saw the videos say there's nothing alien about it. What they saw, and what everybody else who either saw the "alien city or mothership" in person or on videos, was a fairly common natural illusion that goes by the ungainly name of "Fata Morgana."

Fata Morgana is a phenomenon in which distant objects appear to look like gigantic. The optical phenomenon occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion in which an "atmospheric duct" has formed.

A thermal inversion is an atmospheric condition where warmer air exists in a well-defined layer above a layer of significantly cooler air.

A Fata Morgana requires a duct to be present. Thermal inversion alone isn't enough to produce this kind of mirage.

While a thermal inversion often takes place without there being an atmospheric duct, an atmospheric duct cannot exist without there first being a thermal inversion.

TagsFloating City, Yueyang, Foshan, china, UFO, alien mothership, Fata Morgana