People in the area of Cape Town, South Africa saw cloud formations on Sunday that brought comparisons to UFOs.

Not an unheard-of phenomenon, disc-shaped Altocumulus Standing Lenticularis clouds were spotted in the sky — and, as to be expected, captured on social media:

Lenticular clouds over Cape Town, South Africa.

Striking as the clouds are in appearance, the National Oceanic and Atmospheric Administration explains that these are nothing strange, developing when fast moving air is pushed over a land barrier oriented in a perpendicular direction to the air, creating a wave of gravity downwind of the barrier. When the air above the barrier level is moist enough, ACSL clouds will crest where the air rises in these waves (read the full description here.

As for any threat potential, aside from turbulence for aircraft, it’s mostly just an easy photo op for people on the ground.

Photos via @mijlof on Instagram, fdecomite / Flickr Creative Commons