Chasing rainbows

Flanders Moss NNR

It’s been a soggy old autumn on the bog, with the team rarely out of waterproofs and wellies. We’ve become intimately acquainted with the different types of rain, from fine smirr to heavy downpours. But every now and then, when the sun shines, we get rainbows – and Flanders Moss is good at rainbows.

The large, flat expanse of bog and its dramatic mountainous backdrop to the north are a perfect combination for rainbow lovers and admirers of big skies.

If one rainbow is good, two are better: but have you ever properly looked at a double rainbow?

You’ll notice that the primary rainbow is more intense in colour, with the secondary rainbow being more faded, and appearing slightly higher than the primary rainbow.

A (very brief) physics lesson – because the science behind rainbows is fascinating. A rainbow is formed by sunlight entering raindrops. As light enters the raindrop, it is refracted (or bent), such that different wavelengths become visible as colours. These light waves hit the back of the raindrop, which acts like a mirror and reflects the refracted light back out towards us – giving us our rainbow.

The so-called primary rainbow has the familiar colour sequence: Red, Orange, Yellow, Green, Blue, Indigo, Violet. Some of you may remember from school that: Richard Of York Gave Battle In Vain.

However, in the case of a secondary rainbow we find that Vain In Battle Gave York Of Richard! – the colour sequence is inverted.

In this instance, not all of the light is reflected straight out of the raindrop. Some of it remains trapped within the raindrop, and is then reflected an additional time, before leaving the raindrop at a different angle. This double reflection means that the light is refracted again, leading to an inversion in the colour sequence. This explains ‘VIBGYOR’, as well as the faded nature of a double rainbow, and it appearing 9 degrees above the primary rainbow.

A rainbow isn’t a static object however, and all of this depends upon the position of the observer.

As to whether two rainbows means two pots of gold?… well, you’d have to find out for yourselves. But we’d warn you; it’s soggy out there.

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