What atmospheric phenomenon causes refraction of light, resulting in a rainbow?

The phenomenon that causes the formation of a rainbow is the refraction of light through raindrops, which are essential in scattering light into its constituent colors. When sunlight encounters a raindrop, it bends or refracts as it enters and exits the droplet. This bending happens because light travels at different speeds in air and in water, causing the light to change direction.

As light refracts, it also disperses into its component colors—red, orange, yellow, green, blue, indigo, and violet—creating the spectrum observed in a rainbow. The arrangement of the colors is determined by the angle at which the light is refracted. This interplay of refraction and dispersion in numerous raindrops is what ultimately results in the beautiful arc of colors that characterizes a rainbow.

In contrast, while cloud cover may contribute to the conditions for rainbows, it does not directly create them. Sunlight reflection refers to light bouncing off surfaces and does not involve the bending of light, which is crucial for a rainbow. Fog formation also involves tiny water droplets in the air, but it does not provide the same specific conditions necessary for a rainbow to be observed—as fog typically diffuses light rather than refracts it to create distinct colors.