How to Navigate with Rainbows

Many people believe that a thing must be either beautiful or practical. But nature brims with examples that manage both. Rainbows are pretty, but they can also help us to navigate, forecast the weather and tell the time.

Every rainbow we see has three ingredients: a fairly low sun, some rain and us. Rainbows need an observer.

Rainbows appear when we have the sun behind us and rain in front of us. But we can be more specific; rainbows form an arc that is part of a circle. If we imagine the full circle then the centre will be exactly opposite the sun, in a precise spot known as the ‘antisolar point’.

Knowing this allows us to navigate using rainbows, they are in the west near the start of the day and the east near the end of the day. And it is surprising how often we can see the rainbow but not the sun – they’ve got me out of trouble on a number of occasions.

It also makes short term weather forecasts possible. Since our weather tends to come in from the west, a rainbow in the morning is a sign that we’re about to get wet and one in the afternoon is a sign that things will clear soon. And we can go one better – every colour in the rainbow tells us something about the type of rain out there. The more red you see, the bigger the raindrops – ‘Lots of red, means a wet head.’

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Weather Lore

What are Supernumerary Rainbows?

The Secret World of Weather – The Book