Optical Phenomena Rainbow

Optical Phenomena: Rainbow By far and large, the rainbow is one of nature’s most spectacular masterpieces and an excellent demonstration that sunlight is composed of a band of wavelengths each with a distinct color (Henderson, 2016). The rainbow appears as a bow or an arc-shaped spectrum of prismatic colors in the sky opposite the sun from the observer’s perspective, particularly after the rain. It is caused by both the refraction and reflection of the sun’s rays by rain droplets suspended in the atmosphere (Williams, 2013, p. 11-13). This aspect explains why rainbows are only visible when the sun is hanging low in the sky, usually late in the afternoon – in which case it will be to the east of the observer – or seen early in the morning – in which case it will be seen to the west of the observer. To view the rainbow, one need to face away from the sun and look above the ground into the region of the atmosphere covered with suspended water droplets after rain or with a light blanket of mist. In this part of the atmosphere, each suspended individual droplet of water acts as a tiny prism that not only refracts the light from the sun but also reflects it back to the eye of the observer. Therefore, as one sight into the sky, rays of light each concomitant with a particular color is perceived from the collection of the water droplets. This optical reflection results in a colorful circular arc of ROYGBIV (red, orange, yellow, green, blue, indigo, violet) across the sky (Henderson, 2016) (Image 1). Sometimes due to double reflections and refractions of light, a secondary rainbow, which is distinctly larger and paler than the primary rainbow with the colors reversed (VIBGYOR) appear within the original arc. It has so far been established that a rainbow is neither a ‘thing’ nor an ‘object’ and does not exist in any particular locale but is rather an ‘optical phenomenon’ that appears in the sky when sunlight and atmospheric conditions happen to be in the perspective of the observer. Thus, the prime condition for the spectacle to take place requires water droplets and sunlight. Because the suspended water droplets have different optical density than the surrounding atmosphere, it acts as a refractor of light. As the rays cross the air-water droplet interface, it decreases in speed upon entry into the water droplet, reflects, and then refracts (bends away) as it drives through and exits the drop (Henderson, 2016). During this process, the different colors of the white light bend and change to travel at speeds proportional to their characteristic wavelength – with red moving fastest and violet slowest. In other words, the visible light scatters into its constituent seven colors, bounces (reflects) out of the droplet and the rainbow is created. Because sunlight is made up of several wavelengths (or colors) of light, these wavelengths bend at different rates – with some bending more than the others when the lights enter a medium of different density from another. In the ROYGBIV spectrum, red – the longest wavelength – bends the least while violet – the shortest wavelength of the visible light – bends the most. Therefore, when the sunlight upon entering the water droplets exits, it is separated into its constituent wavelengths (colors) of the rainbow with Violet on the bottom and Red on top of the arc. Even though the rainbow appears on the ground as an arc, in the right conditions, and at greater heights, it is a complete circle (Henderson, 2016).