We all know that light follows Rectilinear Propagation and it sometimes bend while diffraction, but i never understand the concept of rainbow and the reason why it is a curve. I have read books and all and everywhere it says that white light passes through raindrops and boom! It is now a circular arc of 7 lights. I understand the phenomenon of refraction and know light of different wavelengths separate when passes through a prism. But after passing through prism, those light travels straight.
But why is rainbow curve? 🌈
In: 21
What happens is light will bounce inside tiny droplets of water suspended in the air. This will send back light with a different direction from which it entered, and this change tends to accumulate light in a specific direction. This direction is defined by the angle between the entering light and the one exiting, and will varies gradually with the light wavelength, so colors end up separated.
Then imagine yourself looking at the sky. The light from the sun can be seen as coming from a single direction, since the sun itself is very far. if your gaze is like a straight line, all the parts of the sky that sits on the special angle between it and the sun direction form a cone.
The reflected light will come from this cone, and from your point of view create a circle. Of course most of the time you will see only half of it and it becomes the very well known bow.
The light that was accumulated into the rainbow will not be visible at other angles, and this creates darker parts of the sky near the rainbow itself.
[A very complete explanation can be found here](https://www.youtube.com/watch?v=M90XEREe66s) (expect a bit of math)
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