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What is a rainbow?

We all love rainbows. Even though we take it for granted that the sky changes colour all the time, there's something about these enormous semicircles that makes us want to smile, point and take photographs. And they're worth looking at, because you're seeing nature's paintbox directly. The entire spectrum of visible light is in there, and every single thing that we can see comes to us as a combination of those colours.

The next few days could be great for rainbow appreciation, especially on Saturday and Sunday. A mixture of sunshine and rain is forecast for all of the UK, as several weather fronts pass over us.

So keep your eyes on the sky, and if you see bright sunshine appearing suddenly after a shower, turn away from it so that you are facing your shadow. If you're lucky, you'll then be looking at a giant arc of colour.

A rainbow is a beautiful example of physics in action. The only ingredients are direct sun and water droplets (rain or mist) some distance away. When sunlight travels into these water droplets, it changes direction (this is called refraction) and the important part is that the path of blue light is bent a bit more than red light. We see sunlight as white, because it's a mixture of all the visible light colours. When sunlight goes into water droplets, bounces off the inside once and then comes out, the blue light comes out at a slightly different angle to the red light. You can only see a rainbow when the sun is behind you, and that's because the light that goes into those droplets and bounces once comes out at about 40 degrees to the direction it went in. The different angles of red and blue light mean that you have to look a bit higher up to see droplets which are sending red light in your direction - that's why red is on the outside of a rainbow.

A rainbow is a very personal thing. Imagine a line that comes from the sun, goes through your head and then keeps going forwards in front of you. You will see a rainbow 40-42 degrees away from that line, and it would be a full circle if the ground didn't get in the way. But the person standing next to you is seeing a different rainbow, because the line joining their head and the sun is a different line. They see the colours from different droplets. You are the only person who can see your rainbow. This is why you can never get to the end of a rainbow - if you move closer to where you think the end is, the rainbow you see is a different one and you can't touch that one either.

If you can't wait for the next shower to see all this, it's easy to make your own rainbow. All you need is a sunny day and a garden hose. I had a go last weekend with my mum wielding the hose (she also saw it as an opportunity to water the garden), and the photo I took is below. Stand with the sun behind you - the lower it is in the sky, the better - and get your helper to spray water a couple of metres in front of you. The shadow of your head will be at the centre of the rainbow circle. It'll be easier to see the rainbow if there's a darker background - in the photo below you can see that the rainbow is easier to see against the darker plants. A rainbow in the sky is exactly the same, but bigger because it's further away.

Even though a rainbow looks ethereal and delicate, bear in mind that the energy from the sun carried by those colours is what powers our world.

If you happen to spot any rainbows over the next coming days, send them to 23degrees@bbc.co.uk

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