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Kid's Science: Prisms and Rainbows

Observing a rainbow arching over the sky can be an awesome experience. If you stop to consider the science behind a rainbow, you'll likely gain a new appreciation of how light travels. All of the conditions need to be just right for rainbows to appear. When sunlight refracts and reflects through raindrops, rainbows appear. Seeing a bow of brilliant red, orange, yellow, green, blue, indigo, and violet stretching above you can be a beautiful sight.


Scientifically, light is part of a spectrum of electromagnetic radiation. Electromagnetic energy also includes radio waves, microwaves, infrared radiation, ultraviolet light, X-rays, and gamma rays. Visible light is electromagnetic radiation in a specific range of wavelengths that human eyes can see. Red light has a wavelength of 0.0007 millimeters, and violet light has a wavelength of 0.0004 millimeters, with the other colors ranging between the two. Light rays travel at 186,000 miles per second in straight lines from their source. It's possible to control light in three different ways: by blocking it, by reflecting it, and by bending it. Reflecting light involves changing its path by using a mirror. Bending light is also called refraction, and this involves changing the light's direction by making the light pass through a material, such as water, that has a different density than air.


Sir Isaac Newton studied how light passes through a prism, and he also identified the colors that make up the visible spectrum, which are red, orange, yellow, green, blue, indigo, and violet. A prism is an optical element that is transparent and has flat, polished surfaces, which can be used to cause light to refract. A prism must have at least two surfaces with a specific angle between them. The degree of the angle determines the degree at which the light's path bends. A dispersive prism disperses light into the visible spectrum or spectral colors, which are the colors of the rainbow. How we perceive these colors involves opponent neurons in the retina that are stimulated by incoming light. The brain then receives a message to perceive the color. Some colors consist of hue combinations that have light frequencies that the human eye automatically cancels out. Examples of these forbidden colors include red-green and yellow-blue. When these combinations occur, the brain decodes them by canceling one of the component parts, so they're not perceived simultaneously.


When sunlight passes through falling raindrops, rainbows can appear that are created by refraction and reflection of light. Raindrops behave like small prisms, so they bend the different colors of the sunlight and disperse them out into a band of colors that appears as a rainbow. Water is denser than the surrounding air, and when the light moves out of raindrops, it moves into separate wavelengths. The light seen by the human eye is made up of different wavelengths, each showing as a different color of the rainbow. The different colors of light bend at different angles, which is why rainbows look like they form an arch shape. Sometimes, it's possible to see a double rainbow, which usually includes one main rainbow and a second paler one. If you look carefully at a double rainbow, you'll notice that the second rainbow is reversed compared to the main one: The red band will be on the inside of one arc and on the outside of the other arc.

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