Rainbows

Hello readers! So yesterday, I thought that I would risk a quick trip to Asda on foot and also to drop off some recycling at their recycling point. But as luck would have it, it poured rain pretty much from the moment I closed the door to when I got to Asda. I also chosen that time to not bring an umbrella out of my sheer hubris thinking I will not need one and I don't wear hoods because...well it messes up my hair. Regardless, the rain made sure it got messed up. But on the way back, when sunlight streamed through the dark clouds, and lit up the wet pavement in little sparkles, I looked around and there was a lovely curving rainbow, streaming colours from the pavement all the way up over the sky. Nature is so cool! I just wish it didn't have to ruin my hair. So this little story moves me into my next post which is about rainbows!



What are they?

A rainbow is an is an optical and meteorological phenomenon caused by both reflection and refraction of light in water droplets in the Earth's atmosphere, resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun. A primary rainbow's arc  shows red on the outer part and violet on the inner side. This is caused by light being refracted (bent) when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it. However, in a double rainbow, a second arc is seen outside the primary arc, and has the order of its colours reversed, red facing toward the other one, in both rainbows. This second rainbow is caused by light reflecting twice inside water droplets.

How are they formed?

To understand the formation of rainbows, you also have to understand the formation of light. Light is made up of a collection of many colors: red, orange, yellow, green, blue, indigo, violet. A prism can take in white light on one side and produce its own mini-rainbow on the other side. A prism is a triangular piece of glass or plastic. To get it to produce a mini-rainbow, you allow a narrow strip of white light to fall on one face of the triangle. This dispersion of colors in a prism occurs because of the refractive index of the glass. So when light enters a material, the difference in the refractive index of air and glass causes the light to bend. The angle of bending is different for different wavelengths of light. When white light moves through the two faces of the prism, the different colors bend different amounts and in doing so spread out into a rainbow.

In a rainbow, raindrops in the air act as tiny prisms. Light enters the raindrop, reflects off of the side of the drop and exits it. So in this process, it is broken into a spectrum just like it is in a triangular glass prism. 

The angle between the ray of light coming in and the ray coming out of the drops is 42 degrees for red and 40 degrees for violet. From this angle, it causes different colours from different drops to reach your eye, which forms a circular rim of colours in the sky which is what we know as a rainbow. In a double rainbow, on the other hand, the second bow is produced because droplets can have two reflections internally and get the same effect. The droplets have to be the right size to get two reflections to work.

Thanks for reading!