Pääsateenkaari

Pääsateenkaari, meaning "main rainbow" in Finnish, refers to the primary and brightest arc of color seen in a rainbow. It is the most commonly observed and recognizable rainbow. The colors in the primary rainbow are always arranged in the same order, from red on the outside to violet on the inside. This order is due to the way light is refracted and reflected within water droplets. Sunlight enters a raindrop and is refracted, then it reflects off the back of the droplet, and finally refracts again as it exits. The different wavelengths of light (colors) are bent at slightly different angles during these refractions, causing them to separate into the familiar spectrum. The red light is bent the least, appearing on the top (outer edge) of the arc, while violet light is bent the most, appearing on the bottom (inner edge). Secondary rainbows, if visible, are fainter and appear above the primary rainbow, with the color order reversed.