What is a fogbow and why are they so hard to spot?

Fogbows are more subtle and muted versions of their brash cousin, the rainbow. A picture of a stunning fogbow was recently captured on Rannoch Moor in Scotland.

Fog is made from tiny droplets of water in the air that are about 0.001 to 0.01mm across. They form a vapour in the air that scatters light that passes through it.

When these tiny droplets scatter light, they can give rise to a range of beautiful weather phenomena. One is the fogbow, which is very closely related to the rainbow.

"A rainbow is still produced by the droplets within mist or fog. But although it will still show the distinctive shape, there is no longer any colour in the fogbow," says Carolin Crawford of Gresham College in the UK.

This is because the size of the droplets are too tiny to bend light very much, so the colours don't split out into the characteristic rainbow pattern. This means the fog bows appear either colourless or with very muted colours.

The best chance of spotting a fogbow is in an even mist, facing away from the Sun. They are hard to spot due to their ghostly colours. For the best chance of spotting one, head to northerly latitudes or keep an eye out in mountainous regions.