The only time I have ever seen a fog bow is very early one summer’s morning, as we were driving towards Loch Awe and Taynuilt in Argyll. The mist was lifting quickly against a brilliant blue sky, and suddenly we saw it hovering there in front us, ghost-like. Less than a minute later, it was gone.
Fog bows follow same laws of physics as rainbows, with a few vital differences. They require a combination of mist and bright sunshine, and the sun must be less than 40 degrees above the horizon.
Because the water droplets in the mist are so tiny, they are unable to split the rays of sunlight into a distinct spectrum of colour. The coloured bands are diffracted or scattered, creating a wide but hazy bow whose centre is the ‘antisolar point’, i.e. the point opposite the sun in the sky.
You can find out more, and see examples of fog bows, at www.atoptics.co.uk.
Photo copyright © Jo Woolf