Rainbows
Rainbows are a spectacular seven-colored phenomenon of the skies that one can marvel at when they set their eyes upon one after a rain. However, the scientific factors that influence the formation of rainbows is often a greater aspect of fascination.
Rainbows are formed when light from the sun is scattered by water droplets, hence why they only form in the presence of sunlight in an environment with sufficient water in the air. The process through which the water droplets scatter sunlight is called refraction.
For a rainbow to be visible, one must have their back to the sun because the refracted light that forms a rainbow bends back towards the direction of the sun and one must be in the path of light in order to view it.
Rainbows are a product of refraction and reflection of light, both of which involve altering a light wave’s direction. Refraction is the process of bending light, while reflection is the process of bouncing light off of smooth surfaces like water. Below is an image of how a water drop refracts sunlight.
The refractive index of the water droplets is the deciding factor of a rainbow’s radius. The refractive index is the amount that a light wave bends as it passes from air to the surface which it refracts, which is water in this case. Water droplets with a higher refractive index will create a smaller and narrower rainbow. Rainbows formed by sea spray will often be smaller than rainbows formed due to salt water having a higher refractive index than fresh water.
Rainbows may seem like half circles but they are truly full circles. When viewed from the ground, rainbows are obstructed by physical features. Occasionally, when viewed from aircraft, rainbows are full circles because being in the sky eliminates physical obstructions that create the illusion of rainbows being semicircles. Below is an image of a full-circle rainbow seen from the sky.
During refraction, the light color with the longest wavelength is refracted the least while the light color with the shortest wavelength is refracted the most. This is the reason why red is always at the top of a rainbow while violet is always at the bottom.
