What is a rainbow and why do we see them?

Rainbows are brilliant, aren’t they!?

What is a rainbow? Well, a rainbow is made from light and water – with help from the Sun. Sunlight is refracted (bent), reflected (bounced off the inside) and then refracted again through droplets of rain, splitting it into the colours that we see (red, orange, yellow, green, blue, indigo and violet).

However, you have to be in the right place at the right time! To see one, you have to be between the Sun and the rain (with your back to the Sun) AND for all of these to be aligned so that the Sun, your eyes and the centre of the arc of the rainbow are in a straight line!

As this tends to mean we can only see a rainbow in the morning or late afternoon, you can work out where to look if conditions are right: a morning rainbow appears when the Sun shines in the East, and the rain falls in the West, and an afternoon rainbow appears when the Sun shines in the West, and the rain falls in the East.

The other day I was on my early morning stroll to work when for a few brief minutes this amazing rainbow graced the sky.


A rainbow, September 12th 2011

We often take what we see in the sky for granted and many people just ignore such cool things as rainbows. I love seeing things like rainbows.

When I was on a skiing holiday in the French Alps a few years back I got to see an amazing ‘rainbow halo’ and ‘diamond dust’ (it’d be great if someone could confirm what these images really show). These pictures don’t really do what I saw justice, but give you some idea of the cracking things you can see if you keep your eyes peeled. The winter Sun was just starting to burn through the morning mist and I got to see these mind-blowing optical effects.

Rainbow Halo

Rainbow Halo, 25th January 2007

Here’s another view:

Rainbow Halo and Diamond Dust

Rainbow Halo and Diamond Dust

And another:

Rainbow Halo and Diamond Dust

Rainbow Halo and Diamond Dust

If you like this kind of stuff too, you’ll love The Cloud Appreciation Society!

*Updated on 26 September 2011

Here are three pics of a rainbow in Glasgow taken this morning about 8am:

Glasgow Science Centre and rainbow

Glasgow Science Centre and rainbow on 26th September 2011

Rainbow over Glasgow

Rainbow over Glasgow on 26th September 2011

Glasgow Tower and rainbow

Glasgow Tower and rainbow on 26th September 2011

*Updated 6th October 2011
Would you believe it!? The first image showing a quadruple rainbow has been captured. Read all about it on the BBC News website.

About Derek Shirlaw

I'm passionate about science communication, social media, and my home country, Scotland. In particular, I have a real interest in astronomy, digital marketing, and the great outdoors.
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  1. Pingback: Derek Shirlaw » September Skywatching from Glasgow, UK

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