Weird Costa Rica cloud formation: Mystery explained.

Costa Ricans were awestruck earlier this week, when a strange, multi-colored cloud appeared in the sky over Escazu.

The rainbow-like cloud inspired amazement in residents – with one observer proclaiming that the weird formation signaled the end of the world, the Washington Post reports.

“The skies opened up as if it were the end of times,” Jessie Montealegre who recorded the rare sky event wrote on Youtube.

“Suddenly a massive amount of people stopped and stood still as they were astonished at how the skies opened up. It was a nice coincidence that the video was taken on Costa Rica's Independence Day," Montealegre said. 

But among atmospheric scientists, there's no mystery here – and certainly no dire prognostication.

The striking phenomenon is scientifically known as cloud iridescence. After a similar iridescent cloud appeared over Boulder, Colo., in 2007, NASA explained the science behind the meteorlogical event:

“These clouds are formed of small water droplets of nearly uniform size. When the Sun is in the right position and mostly hidden by thick clouds, these thinner clouds significantly diffract sunlight in a nearly coherent manner, with different colors being deflected by different amounts. Therefore, different colors will come to the observer from slightly different directions.”

Angela Fritz further explains this cloud formation in the Washington Post,

This is a pileus cloud, sometimes called a “cap” cloud because of the way it caps the top of the cumulus cloud. They typically form during the early stages of thunderstorm development, when a strong updraft of rising air is present in cumulus clouds. The upward motion of the building cumulus cloud causes the whole layer of air above the storm to rise. The moisture in this thin layer cools and condenses into cloud droplets, which forms the wispy, flat cloud that caps the storm.

The best way to spot these clouds are during the early stages of thunderstorm development, but you have to be vigilant since they don’t typically last very long. The iridescence can be seen when the sun is positioned behind the building storm clouds so that the refracted light can pass through the pileus and to your eyes.

This week’s phenomenon, was visible in skies over a number of cities in Costa Rica, including San Jose, Parrita, Pavas, Escazu and Hatillo, according to ABC News. 

Iridescence is just one of many optical phenomena that exists when the sunlight interacts with clouds. Earlier this summer, western Wisconsin residents were dazzled, when a rare, rainbow-like cloud occurred across the sky.

Colloquially referred to as a fire rainbow, the optical phenomenon is neither a fire nor a rainbow. It occurs when sunlight refracts through plate-shaped ice crystals, according to weather.com.