What I saw on my holiday – Part 2

Now the summer is coming into its own (in a very rainy way here in England) Science Burrito brings you the sequel of to the Holiday Blog. Last time I showed you the glory of rainbows and a pretty little bird. Where will we go this time?

Sticking with the theme of light, because, hey, it’s what I do, have you ever asked “Why is the sky blue?” It’s meant to be a pretty common question kids ask, so you probably have at some point in your life. Many of you may know, many of you may not, that it is because of something called Rayleigh Scattering, and it is very similar to what makes a rainbow, but also it is entirely different.

When we learned about rainbows, we saw that light bounces around inside the water droplets in the air and they spread the white light into a rainbow. In the sky, the tiny particles that float around in the air (I mean really tiny, not like the dust you see in a sun beam, really, really, tiny, so tiny you can’t see them) ‘scatter’ the light that hits them. This means that, instead of bouncing around the inside of the water droplets, the light bounces around the outside of the air particles.

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Just like in the water, different colours of light are ‘scattered’ different amounts, so blue is scattered a lot and red not very much. So, when the sun is high in the sky, the light going past above your head is scattered and the blue light comes down towards you and the red light ploughs out on into space.

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When it gets to sunset, the light goes through the atmosphere to get to you and the blue light is scattered away from you and the red light gets through to your eyes, so sunsets look red.

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In between the two all the colours of the rainbow can be seen.

So, while I was on holiday, I snapped this little photo.

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The clouds at the top look white, like normal, but the ones underneath look pinky orange. Now, we’ve all seen pink clouds around sunset or sunrise, I’m sure, and now you know why, but I took this photo in the middle of the day. So what’s going on here?

What I just told you about tiny, tiny particles scattering light is only true for very, very tiny particles. Bigger particles don’t do it. They only scatter light according to their colour (because they absorb all the others colours and reflect the colour you see). That’s why clouds are usually white, because they are made of steam. And sand, which is a yellow/orange colour, only scatters that colour light.

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Now, it was a really windy day when I took this picture, so the air was full of sand. So, even though you can’t see it really, there is enough sand low down in the air to turn the clouds a kind of pink colour. But way up high in the air, there was less sand and the clouds appeared white, as normal.

I also took this picture of some palm trees, because palm trees are pretty. Everyone relax and look at the palm trees. Ahhhhh.

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