Late on Sunday afternoon, snap-happy Instagrammers in Cape Town were treated to an eerie and wonderful spectacle, as dark disc-like objects loomed over the surrounding mountaintops, like something out of a Hollywood Sci-Fi film.

Luckily, there was no ensuing alien invasion. These so-called “UFO clouds” are actually “lenticular clouds” – the name comes from the Latin word meaning "lens-like." Although, you can definitely see where the nickname "UFO clouds" came from.

These types of clouds typically form when high, humid winds blow over mountainous terrain, such as the Table Mountain overlooking Cape Town. When they pass over these mountains, the air tends to cool, which makes the water vapor condense into droplets. Although the air is always flowing, the spot where the moisture condenses stays stationary. The flow of the surrounding wind simultaneously "carves" this area of condensation into a disc-like shape. 

[H/T: National Geographic]

^{Main image credit: Kyle Mijlof/@mijlof/Instagram}