A bizarre rainbow-colored halo spotted over Pu'er in the Yunnan Province of China left netizens scratching their heads. A photograph of the formation went viral and kicked up a storm on social media.

The image shows a large halo of colors around an ominous-looking dark cloud. Captured by photographer Jiaqi Sun in late August, a Facebook page called "NASA picture of the day" shared the image and offered a scientific explanation for the rare occurrence.

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"Pictured, behind this darker cloud, is a pileus iridescent cloud, a group of water droplets that have a uniformly similar size and so together diffract different colors of sunlight by different amounts," the post explained.

An iridescent pileus cloud is formed when water vapor particles warmer than the surrounding air move upward to form a cumulus cloud. It pushes air above in layers, in a cauliflower-shaped formation.

These air layers expand and cool which leads to the condensation of the water vapor into droplets. A thin layer of cloud is formed, positioned as a pileus, or a cap, atop the rising cumulus.

A cumulus cloud is detached and separate. It is usually observed in fair-weather conditions and is formed due to convection.

NASA, too, joined the discussion and agreed that it is indeed an unusual phenomenon.

"Also captured (in the photo) were unusual cloud ripples above the pileus cloud. The formation of a rare pileus cloud capping a common cumulus cloud is an indication that the lower cloud is expanding upward and might well develop into a storm," NASA wrote on its "Astronomy Picture of the Day" website.

This explanation, however, was not sufficient for conspiracy theorists. Rumors of an explosion, emission of toxic chemicals, and even a Chinese government hologram experiment were put forward.

Recently, another bizarre sky phenomenon was noticed in the South American country of Chile. Beautiful red streaks observed in the night sky were captured in the Atacama Desert near the European Southern Observatory's (ESO) La Silla Observatory. These red streaks are called red sprites, and they are a type of lightning occurrence.

"During the day, sunlight knocks electrons away from nitrogen and oxygen in Earth's atmosphere and, at night, these electrons recombine with the atoms and molecules, causing them to shine," ESO said in a news release.

A rainbow appears on the Auckland skyline featuring Sky Tower in New Zealand
NASA