I was really surprised when I got to know that a rainbow is actually a circle! Yesterday, after having observed a vivid rainbow in the sky I had a strong curiousity to get to know more about this phenomenon.
But let me be consistent in the explanations.
As strange as it may seem, but a rainbow is not a two-dimensional object. It is a three-dimensional occurrence that is composed of huge quantity of droplets. This is one of the main ideas to the explanation why rainbows are curved.
The picture below shows schematically «how a rainbow works»: drops are floating in the air collecting the scattered light at a definite angle regarding the initial way of light coming from the sun. The angle is 40-42 degrees depending on wavelength.
So as we look at a rainbow, there is a kind of a horizontal cone formed with our eyes in the role of its top.
By the way, one of the conditions of a rainbow is that is appears on the other side than the sun. It means that one can observe a rainbow only standing with his back to the sun. Scientifically it is called the antisolar point. The sunlight is directed to the drops of a cloud and jumps back at an angle of 40 degrees as I said before. It is true that light beams bounce back in different directions, just a person sees the ones that fit into this 40 degrees space.
The height of the rainbow is the issue of how high the sun is in the sky.
As well, the picture shows that there is an invisible part of the rainbow. It is really so when a person looks at the rainbow from ground and horizon prevents to observe it in any other way, but the situation changes if a rainbow is seen from the sky. All the pilots know that rainbows are actually circles! It is amazing, isn’t it?
One more interesting phenomenon is a double rainbow.
In each droplet light is reflected and refracted: it penetrates them, is refracted and reflected off their back part and then it leaves droplets again refracted. This is how it looks like:
I think everybody has noticed that the second rainbow is much fainter than the primary one. It is explained by physical fact that some light is lost every time it goes inside drops. When there is one more light reflection inside waterdrops, it creates the second rainbow in the sky which appears to be higher at 50-54 degree.
Have you ever noticed that in the secondary rainbow the colors are reversed, starting from violet and finishing with red? No? Now you know this.
Such simple natural things are so interesting to be explored. Let us do it together! Stay with me!