Scientists: China's city in the sky was a weather-based optical illusion

JIANGXI, China, Oct. 20 (UPI) -- Meteorologists said a city in the clouds spotted by thousands of residents over two southern Chinese cities was an optical illusion known as a Fata Morgana.

Shapes that resembled a cluster of skyscrapers were reported by residents and caught on video over the cities of Jiangxi and Foshan earlier this month, and online theories ranged from an alleged secret NASA plot called "Project Blue Beam" to a test of secret holographic technology by the Chinese government.

However, meteorologists said the flying city was likely a Fata Morgana, an optical illusion that distorts distant objects as a result of cool temperatures on the ground contrasting with hotter temperatures high in the air.

Scientists said the result made it appear as if the skyscrapers on the far horizon were floating high up in the sky.

"The illusion is due to a slightly unusual temperature structure in the lower part of the atmosphere," Professor 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."