How does a Rainbow form?
It’s a question that often goes through the minds of children and adults alike when they set eyes on the beauty and wonder of a rainbow....but how many of us ever actually go and find out?
Not many would question the delight to be had when seeing a rainbow. The wonderful sight of a rainbow is one of those things that brings a smile to people’s faces and something we never seem to tire of. But despite always wondering, have you ever actually found out exactly what makes them appear? No? Then let me enlighten you.
Many people know that if you shine a beam of normal white light through a prism, it is split into the many colours, visible and otherwise, that the white light is actually made up of.
Now, raindrops break up light in a similar way. If light is shone into them, from the sun, the light that is reflected off the back surface of the drop, just like light bouncing off the surfaces of a prism, is split into the many component colours that make up the white light.
These different component colours, just like from a prism, spread out and leave the raindrop at different angles. The colour of the light that then actually makes it to your eye depends on what angle that raindrop is between you and the source of light, the sun. Note that when you see a rainbow, you are usually between it and the sun. Remember you are looking at light that has gone through the rain drop and is now bouncing back at you from it's back surface.
A raindrop that is higher up in the sky will reflect red light at just the right angle for your eye. A raindrop that is a little lower in the sky will reflect green light at just the right angle for your eye. Lower in the sky still and a raindrop will reflect blue light to your eye at just the right angle. These three colours are the most dominant when you look at a rainbow. You will normally be able to just make out the other colours, but they are not as easily recognised.
Now, multiply one raindrop by millions, and high in the sky you see a band of red light, lower a band of green, and lower still a band of blue light, and the other colours in between accordingly, although as noted, these three colours are usually the most easily discernible.
And that, is how a rainbow is formed. To complicate things a little though, rainbows are actually full circles, but when viewed from on the ground, we only see the top half, because the horizon gets in the way. It is possible to see the full circle of a rainbow if you are high enough off the ground and have the sun in just the right position behind you.