The traditional explanation of a rainbow.

A rainbow is a meteorological phenomenon that occurs when sunlight is refracted, or bent, as it passes through raindrops in the atmosphere. The sunlight is then reflected off the back of the raindrop and refracted again as it exits the raindrop, creating a spectrum of colors that form a circular arc in the sky. The colors of the rainbow, in order from the outer edge to the inner edge, are red, orange, yellow, green, blue, indigo, and violet. This colorful arc is often seen after a rain shower when the sun is shining and the raindrops are still in the air.

When sunlight strikes raindrops in the atmosphere, it undergoes a process called refraction, which is the bending of light when it passes from one medium to another with a different density.

As sunlight enters a raindrop, it is refracted towards the center of the drop. Inside the raindrop, the light is reflected off the back of the drop. As the light exits the raindrop, it is refracted again, this time away from the center of the drop.

The angle at which the light is refracted depends on the wavelength of the light. Shorter wavelengths (blue light) are refracted more than longer wavelengths (red light).

As a result, the different colors of light are separated into a rainbow. The red light is refracted the least, so it appears at the top of the rainbow. The violet light is refracted the most, so it appears at the bottom of the rainbow.

The position of the rainbow in the sky depends on the position of the sun and the observer. The rainbow is always opposite the sun, and it is always a circular arc. The size of the rainbow depends on the size of the raindrops. Larger raindrops produce smaller rainbows, while smaller raindrops produce larger rainbows.