One of the most beautiful and majestic phenomena in nature are R A I N B O W ! People of all ages awe at this beautiful ring in the sky, as we see the seven coloured bow piercing the clouds.Have you ever wondered what makes a rainbow, how are they formed, is there an end to a rainbow, can you touch it, or create it in your back yard? Well Physics has answers to every question of your's , and of course it leaves you with more questions to think about.



HOW ARE RAINBOWS FORMED?

There have to be three conditions that needs to be satisfied for a rainbow to exist

1. The Sun must be behind you.

2. There must be drops of water(radius about 1 millimeter, since water droplets are spherical because of Surface Tension, the property by which a liquid minimizes its surface area) in the sky in front of you.

3. There must be nothing obscuring the sun from the raindrops, like clouds.



In order to learn more about rainbows, we need to understand something called Refraction. Sir Issac Newton , in his book OPTICKS published in 1704 explained this phenomena.





REFRACTION : When light rays pass through one medium to another(in this case rarer to denser, like air to glass) , they bend , and light slows down. But don't we say speed of light is a constant? YES IT IS, BUT ONLY IN A VACCUM . The speed of light is different in different medium, it is slower in water than in air.



Newton showed that , light not only bends , it splits into 7 colours, thus white light is a mixture of seven colours, which we call Dispersion.(A very non intuitive idea to the artists) : When light rays pass through one medium to another(in this case rarer to denser, like air to glass) , they bend , and light slows down. But don't we say speed of light is a constant? YES IT IS, BUT ONLY IN A VACCUM . The speed of light is different in different medium, it is slower in water than in air.Newton showed that , light not only bends , it splits into 7 colours, thus white light is a mixture of seven colours, which we call Dispersion.



Dispersion of Sunlight into its seven colours in a nearly spherical raindrop



Now as Sunlight enters a raindrop, it refracts , it splits into the seven colors. this refracted light may either leave the drop from the other side, or get reflected. When this light reflects back from the raindrop,it changes its direction and again refracts , splitting further into the seven colors and leaves the raindrop.

This refraction, reflection and again refraction is what creates a rainbow.

The maximum reflected angle for red light is 42 degrees and for blue is 40degrees. Now as Sunlight enters a raindrop, it refracts , it splits into the seven colors. this refracted light may either leave the drop from the other side, or get reflected. When this light reflects back from the raindrop,it changes its direction and again refracts , splitting further into the seven colors and leaves the raindrop.This refraction, reflection and again refraction is what creates a rainbow.



Now, the maximum angle through which red light can bend is 42 degrees. it can be anything between 0 to 42, and the maximum angle foe violet light is 40 degrees. Now each of the different colors have a specific maximum angle, and these light rays at their maximum angle make the spray bands on a rainbow.





You might ask that red light could have a 40 degree angle too, cause its maximum angle is 42 degrees, so it can have any angle between 1 to 42 degrees , right?



Well this is an excellent question, and the answer is that a particular color at its maximum angle has more effect than any other. So blue or violet will be more visible at 40 degrees than any other.



HOW TO SPOT RAINBOWS IN THE SKY.

Right before or after a rainshower, stand in the opposite direction to the Sun, and imagine a line passing from your head to the tip of your shadow. The steepness of this line depends on how high the Sun is in the sky. Noe look at an angle of 42 degrees from this imaginary line, and you will see the red spray, at an angle of 40 degrees, the blue spray is visible , and between them, all the other colors of the rainbow.





Well this explains it easily, since blue or violet is at an angle of 40 degrees from the imaginary line it is always on the inside, and red at 42 degrees is on the outside . All the other spray bands are inside these two, at their particular maximum angles . Also you may notice that the part of the sky underneath the blue band is light blue , and bright whereas above the red band, the sky is dark blue in color. This because since sunlight is reflected at different angles, all the light reflected below 40 degrees is a mixture of several different colors of light, which is white light, thus the part of the sky below the blue band is light. And since no light reflects at an angle more than 42 degrees, most the part above the red band is DARK.



WHY IS THE RAINBOW A BOW AND NOT A STAIGHT LINE?

Well the answer lies in the imaginary line too. Trace an angle of 42 degrees from the imaginary line in all the directions around it and you see its a bow, the color you traced forms a bow in all the directions. But sometimes, actually most of the times we only see a part of the bow. This is because there aren't enough raindrops in the sky to see a complete bow, because of obscuring clouds.



THERE ARE ALWAYS TWO RAINBOWS IN THE SKY? Well this explains it easily, since blue or violet is at an angle of 40 degrees from the imaginary line it is always on the inside, and red at 42 degrees is on the outside . All the other spray bands are inside these two, at their particular maximum angles . Also you may notice that the part of the sky underneath the blue band is light blue , and bright whereas above the red band, the sky is dark blue in color. This because since sunlight is reflected at different angles, all the light reflected below 40 degrees is a mixture of several different colors of light, which is white light, thus the part of the sky below the blue band is light. And since no light reflects at an angle more than 42 degrees, most the part above the red band is DARK.Well the answer lies in the imaginary line too. Trace an angle of 42 degrees from the imaginary line in all the directions around it and you see its a bow, the color you traced forms a bow in all the directions. But sometimes, actually most of the times we only see a part of the bow. This is because there aren't enough raindrops in the sky to see a complete bow, because of obscuring clouds.



There are almost always two rainbows in the sky, primary and secondary. The rainbow which we have been talking about is the primary rainbow , formed when light reflects only once through the rain drop, and the secondary rainbow is formed when light reflects twice through the drop. It is much more fainter than the primary rainbow and because it reflects twice , the colors are reversed. So the secondary rainbow has red on the inside and blue on the outside , The secondary bow is much fainter because very less light reflects twice in a raindrop than ounce, and since it reflects twice , it ha a bigger angle than the primary bow, the red has angles greater than 50 degrees and blue greater than 53 degrees . So whenever you look at the primary rainbow , just 10 degrees to it you will see the secondary rainbow.



Is there a tertiary rainbow?

You might have guessed that the tertiary rainbows are formed by the sunlight reflecting thrice in a drop.Well yes, but it is much more fainter than the other two rainbows and it is centered at the Sun, which makes it more and more hard to look at.



HOW TO MAKE A RAINBOWS IN YOUR BACKYARD?

Its really simple, stand infront of the direction of the Sun with your back facing at the Sun and sprinkle some water through a garden hose or a sprinkler all around you and look at an angle 42 degrees from your shadow and there it is , your own little teeny weeny primary rainbow. And about 10 degrees to that will the secondary rainbow. You could also see a rainbow near a fountain, the concept applies everywhere , 42 degrees the imaginary line passing through the head of your shadow and there is, HURRAY!!!



ALRIGHT, THE FINAL AND THE MOST IMPORTANT QUESTION, ARE RAINBOIWS REAL?

You may wonder if rainbows are real, or just a mirage , an illusion. Well the answer is RAINBOWS ARE REAL! Infact you can even touch a rainbow, its just light, a different colored than usual interacting with water, also rainbows do have an end, its just a very massive circle , and if at the edges there are very few drops, it might disappear. Try touching a rainbow that you create in your garden, its fun! There are almost always two rainbows in the sky, primary and secondary., formed when light reflects only once through the rain drop, and the secondary rainbow is formed when light reflects twice through the drop. It is much more fainter than the primary rainbow and because it reflects twice , the colors are reversed. So the secondary rainbow has red on the inside and blue on the outside , The secondary bow is much fainter because very less light reflects twice in a raindrop than ounce, and since it reflects twice , it ha a bigger angle than the primary bow, theand. So whenever you look at the primary rainbow , just 10 degrees to it you will see the secondary rainbow.Is there a tertiary rainbow?You might have guessed that the tertiary rainbows are formed by the sunlight reflecting thrice in a drop.Well yes, but it is much more fainter than the other two rainbows and it is centered at the Sun, which makes it more and more hard to look at.Its really simple, stand infront of the direction of the Sun with your back facing at the Sun and sprinkle some water through a garden hose or a sprinkler all around you and look at an angle 42 degrees from your shadow and there it is , your own little teeny weeny primary rainbow. And about 10 degrees to that will the secondary rainbow. You could also see a rainbow near a fountain, the concept applies everywhere , 42 degrees the imaginary line passing through the head of your shadow and there is, HURRAY!!!You may wonder if rainbows are real, or just a mirage , an illusion. Well the answer isInfact you can even touch a rainbow, its just light, a different colored than usual interacting with water, also rainbows do have an end, its just a very massive circle , and if at the edges there are very few drops, it might disappear. Try touching a rainbow that you create in your garden, its fun!



