A Rare Monochrome Rainbow over County Clare

Imagine this…

It’s a gentle Spring evening in County Clare, Ireland. A delicate rain is moisturising the Irish countryside as a white horse grazes in a pasture.

The sun is setting over the Atlantic, and just for a few moments, the mist in the air and the angle of the sunset combine to create what in meteorological circles is known as a “monochrome sunset.”

That’s when the rainbow appears to be just one colour — usually a brilliant red.

While Ireland is well known for its rainbows, the incidence of a single-colour “monochrome” rainbow is quite rare and requires just the right conditions.

So who stole the other colours of the rainbow?

It’s an optical illusion, just like the multi-coloured arcs of light.

It all has to do with particles and moisture in the atmosphere refracting and reflecting light. The angle of the sun and how the light strikes the water droplets determines the prismatic effect.

A monochrome sunset is usually seen at sunrise or sunset during rainstorms when the sun is low in the sky.

The low angle of the sun scatters the blue, green and yellow (shorter) wavelengths of light leaving the intense red (longer) wavelengths for our visual enjoyment.

So the next time you see a rainbow, think of those rays of light bouncing around and splitting into colours, and never stop searching for the pot of gold!