Question

why the shape of rainbow is parabolic?

Answer 1

Well, a rainbow is actually circular in shape. It is not shaped like a semicircle or an arc or a parabola. We can’t see the full circular shape because the horizon cuts off the lower half or we can say that our range of vision is cut off by the horizon. But if we reach to a sufficient height, without any disturbance, then we would be able to see a full circular rainbow.

A rainbow needs two things for its formation- water droplets and sunlight. Under the appropriate conditions, each water droplet acts like a prism. So when a beam of sunlight hits the droplet, two things can happen: Either the light will simply pass through, or it will bend across the surface of droplets, bounce off the other surface, and then bend again as it comes out, dispersing the white light into the seven visible colors (VIBGYOR) that make up the wonderful rainbow.

In a nut shell, the appearance of a rainbow depends on where we stand or observe it. If we move, then the rainbow moves. It means for every single person, the view of rainbow will be different. So, the range of angles at which raindrops reflect is the actual reason why rainbows are curved.