If you were in Cape Town yesterday or you happen to spend your time nature-gazing on Instagram, you might well have happened across some of these spectacular and almost ominous-looking images of clouds bearing down upon the famous port city.
But before you start panicking and load up the car with all your old camping gear to head in whichever direction is opposite to South Africa, don't worry – these things aren't UFOs and there is no imminent alien activity that we're aware of (sadly).
These awesome formations are called lenticular clouds (Altocumulus lenticularis) – as their circular shape evokes the appearance of a lens – and they're totally harmless. Lenticular clouds are stationary clouds that form at high altitude, usually near large mountains, a la Cape Town's Table Mountain.
Once stable moist air passes over a mountain or mountain range, large-scale standing waves sometimes take shape on the downwind side. From the crest of these waves, lenticular clouds may form, with moisture condensing in the shape of these distinctive circular plumes.
They don't always look like the ones that appeared in Cape Town this week either. Depending on the atmospheric conditions, lenticular clouds may appear wide and flat, or relatively stout and condensed like the UFO-esque phenomena seen in these photos.
Most spectacularly, sometimes a string of lenticular clouds can form one on top of the other, creating a vast vertical lenticular wave cloud – albeit, not one that looks so much like a watery wave as this stunning formation spotted recently. The lenticular clouds in Cape Town are called stratocumulus standing lenticularis clouds due to their height and shape.
Because of their freaky appearance and disc shape, lenticular clouds are said to have been the subject of numerous UFO 'sightings' over the years, which is actually kind of understandable given they're a pretty rare sight and not the kind of wispy formless cloud most of us are used to seeing dotted across the sky.
Side note: the clouds are also the perfect shape and size to mask an actual circular UFO in a cloud, although the freaky perfection of that UFO-hugging fog does mean they're not the most inconspicuous of disguises. If any aliens are reading this, we'd recommend sticking with your standard invisibility cloak feature - it's more effective, guys.