Astronomy Picture of the Day . Rainbow at Sunset . ... Explanation: Where is the Sun when you see a rainbow? ... The rainbow itself is produced by sunlight internally reflected in rain drops from the direction opposite the Sun back toward the observer . As the sunlight passes through the drops, from air to water and back to air again, longer wavelengths (redder colors) are refracted or bent less than shorter wavelengths (bluer colors), separating the sunlight into the colors of the rainbow. ...