Sateenkaariilmiö

Sateenkaariilmiö, often referred to as the rainbow phenomenon, describes the visual effect observed when light interacts with atmospheric water droplets, such as rain or mist. This phenomenon is responsible for the appearance of a multicolored arc in the sky. The primary mechanism behind the sateenkaariilmiö is the dispersion of sunlight. When sunlight, which is composed of a spectrum of different colors or wavelengths, enters a water droplet, it refracts. Refraction is the bending of light as it passes from one medium to another.

As the light enters the droplet, it slows down and bends. Different wavelengths of light bend at slightly different angles. Violet light, with its shorter wavelength, bends more than red light, with its longer wavelength. This separation of colors is known as dispersion. After entering the droplet, the light travels to the back surface where it is reflected internally. Upon exiting the droplet, the light refracts again, further separating the colors.

The observer sees the sateenkaariilmiö as an arc because of the specific angle at which light of each color is reflected and refracted back towards the viewer. For a primary rainbow, this angle is approximately 42 degrees relative to the direction of the incoming sunlight. Each observer sees their own unique rainbow, as the light rays reaching their eyes originate from different sets of water droplets. The order of colors in a primary rainbow is always red on the outside and violet on the inside. Occasionally, a secondary rainbow, with reversed colors, can be observed above the primary one due to a second internal reflection within the water droplets.