What are those bright rainbow colours in the sky, if not rainbows?
My thanks to Giel Spierings for the following email and permission to share it here:
Hi Tristan,
I’ve been enjoying your book, ‘The Walker’s Guide to Outdoor Clues & Signs‘ and while reading it on a beach near where I live I saw a part of a rainbow in the sky (photos attached) and I tried to find an explanation in your book but couldn’t find it. Would you be able to explain how this formed? I especially can’t understand the one to the west of the sun.
My favorite thing I learnt in your book is telling the time using ‘the plough’ and the north star.
I hope to hear from you.
All the best,
Giel
Hi Giel,
Thanks for your email and for reading my book. You might want to have another quick read of the ‘Sky and Weather’ chapter and the illustrations there, (especially p.131-5 in the paperback). But here are a few paragraphs that you might find helpful:
Excerpt from The Walker’s Guide to Outdoor Clues & Signs (UK) / Lost Art of Reading Nature’s Signs (US):
It is very common to spot a halo around the sun or moon. One will form whenever light passes through ice crystals of the right kind. The most common form of halo is known as a 22˚ halo, which is easy to check – it will be just over two extended fist widths from sun to halo. This halo is a strong clue to there being cirrostratus cloud, which, as we will see, can in turn help warn of an advancing front and possible rain.
On the same level as the sun, but just outside the area where you might see a halo, one of the most frequent sights are ‘sun dogs’, also known as ‘mock suns’ or ‘parhelia’. Sun dogs are the most easily formed of these sky effects and they show up as bright smudges of light, occasionally very bright indeed, and often display a selection of rainbow colours. Sun dogs are a clue to cirrus cloud, even when it is hard to see directly, which likewise can be used as an early warning of an advancing front.
If you see sun dogs, it is definitely worth scouring the rest of the sky. Depending on whether the sun is high or low, you might see marvellous bright arcs with names like ‘circumzenithal’ or ‘circumhorizontal’ arcs. These arcs mean the same thing as sun dogs – there are cirrus clouds high in the sky – but they add yet more colour and often blaze unseen.
You might also enjoy:
Rainbow Natural Navigation Mini Quiz
