If you didn't know better you would think it was the LGBTQIA+ community sending good vibes from the sky
25 Mayo 2018 14:48
The phenomenon of an iridescent cloud occurs when you can see the colours of a rainbow in a cloud. These are beautiful phenomena that are similar to the formation of rainbows, or colour formation in oil coatings in water. It's difficult to spot it when the sun's glare shines on it, so it's best to somehow hide the sun when trying to observe it. Cloud iridescence most commonly happens in altocumulus, lenticular, cirrus, and cirrocumulus clouds.
Clouds in meteorology are considered an aerosol; a mass that you can see made up for tiny liquid drops, icy particles, and frozen crystals that exist in suspension in the atmosphere over the surface of a planet or another celestial body. On our planet, clouds happen when air saturation makes the air cool down to its so-called 'dew point', the temperature at which water vapours become liquid water.
Clouds have been mythologised by various human cultures since antiquity. The Akkadians thought of them as the sky goddess Antu's breasts. One of the comedies of Aristophanes, the ancient Greek playwright, is even called The Clouds. In this play, Socrates proclaims that clouds are the only real gods, and they change their shape to show whoever is looking at the time their true nature. When a politician with long hair looks at them, they turn into centaurs, the embezzler Simon makes them transform into a wolf, and Cleonymus, a coward, compels them into the shape of a deer!
Iridescent clouds happen when particularly minuscule ice or water particles are in the air. If these ice or water particles are bigger, they usually produce lunar or solar halos, which is the giant circular shadow that we can sometimes see forming around the moon or the sun respectively. These tiny particles, however, cause the diffraction of light, which is the same process through which regular rainbows can happen. Their name comes from Iris, which is the ancient Greek embodiment of the rainbow.
Iridescent clouds are quite similar to another aerial phenomenon called a 'circumhorizon arc'. The way to distinguish them is fairly simple once you know what to look for: despite the fact that they are both rainbow-like occurrences in the sky, a circumhorizon arc, as the name suggests, is a band that you can see parallel to the horizon. On top of that, an arc will have an organised arrangement of its colours, while an iridescent cloud has a random distribution.
In addition, circumhorizon arcs look like they're much fuzzier than iridescent clouds as they, much like the sun or moon halos that we mentioned above, form mostly due to ice crystals in cirrus-type clouds. Iridescent clouds, on the other hand, occur mostly because of water droplets.
Finally, for a circumhorizon arc to happen, the sun needs to be way up in the sky, about 58 degrees above horizon level. Cloud iridescence, on the other hand, will appear very close to the sun, hence the need to hide the star if you want to observe them.