The second rainbow is not as bright as the primary rainbow, because some of the sunlight passes through the droplet, while most of it is reflected. This happens when sunlight is reflected twice inside each water droplet and directed back to you. Sometimes you can see a fainter, second rainbow appear above a rainbow. This is why the circle of light always has an angular distance of 40-42° from the antisolar point, meaning a rainbow always appears 40-42° away from the point opposite the Sun, as seen from your perspective. Most of the light is cast back at you in an angular range from 40° for violet light to 42° for red light. This causes the sunlight to be reflected off rain droplets within a limited range of angles that lie between 0° and 42°. The shape of a rainbow is a result of the refractive index of water. It is also possible to see a circular rainbow from an airplane. You may be able to see a circular rainbow if you have a high vantage point and the terrain sharply drops off in the direction of the rainbow, allowing the rain to fall down farther and reflect the sunlight from a lower angle. The lower half of the circle, however, is usually not visible since the water droplets hit the ground before it can form. Technically, a rainbow is the upper half of a circle of light, which centers on the antisolar point, the point directly opposite the Sun, as seen from your perspective. From top to bottom, they are: red, orange, yellow, green, blue, indigo, and violet. This imaginary first, middle, and last name is an acronym made up of the initial letter of each color, in the order they appear in a rainbow. If you are having trouble remembering the order of the rainbow colors, simply memorize the name Roy G. Further below, the droplets form an even sharper angle between you and the Sun, so they throw the yellow, green, blue, indigo, and violet components of the sunlight back at you, creating the remaining stripes of the rainbow. This is how the top two stripes of the rainbow-red and orange-form. For example, you can only see the red light from droplets that are higher in the sky, and only the orange light from the droplets that are a little lower. However, because it reflects and refracts each color at a slightly different angle, only one color from each droplet reaches your eyes. This means each water droplet reflects all of the colors of the sunlight back to you. For example, in relation to the direction of the incoming ray of light, the red light component leaves the droplet at a slightly larger angle than the orange component. Each color is refracted in a marginally different direction, creating the impression of a fan of colors. RefractionĪs the ray of light enters and leaves the water droplet, its direction is also changed slightly in a process called refraction. This happens both when the ray enters the droplet and when it leaves the droplet again. As soon as a ray of sunlight enters a water droplet, it is split up into its components, causing its colors to fan out and become visible as a spectrum of colors. Pure sunlight may appear white to us, but it consists of all visible colors. Reflection, dispersion, and refraction inside a water droplet.īut sunlight is white-so, if the water droplets reflect the sunlight, how does the rainbow gets its colors? This is where the second process comes into play: dispersion of light. During a rain shower, the air is full of water droplets acting together like a reflective curtain made of millions of minuscule mirrors casting the sunlight back at you. When a ray of sunlight strikes one of these tiny spheres of water, most of the light bounces off its rear wall and is reflected back. Water droplets can act like little mirrors. Rainbows can also appear at night How Do Rainbows Form?Ī rainbow is an optical phenomenon which involves three processes: reflection, dispersion, and refraction. So, if you have your back to the Sun, the rainbow will arch across the sky in front of you. Rainbows always appear in the sky opposite to the Sun. The air opposite the Sun, as seen from your position, must be filled with a large number of water droplets.If you are at the same elevation as your horizon, the Sun's altitude must be below 42° to create a rainbow that can be seen from your perspective. The Sun has to be quite low in the sky. ![]() The Sun must be above the horizon and not be obscured by clouds, mountains, or other obstacles.©/constantinopris Low Sun and Water DropletsĪ rainbow can only form under the following conditions: Business Date to Date (exclude holidays).
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