The higher the sun is in the sky, the less of a rainbow is visible above the horizon. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Get smart. Um, what? The visual spectrum — Color theory is a bit more complicated than stirring together the right finger paints. Subtractive color mixing is pretty close to the paint mixing we did in grade school.
Additive color mixing. If you like me have a hard time wrapping your head around how red and green mix together to make yellow, watch this YouTube video.
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Sign me up! Join the community. Current design contests Designers, check out these contests so you can start building your career. Designers, see opportunities. Pin It. The light reflecting back to you, the observer with the Sunlight coming from behind you, from the water droplets will appear separated into all the colors of the rainbow!
Violet will be on the bottom and red on the top. A secondary rainbow appears if the sunlight is reflected twice inside the water droplets. Secondary rainbows are fainter, and the order of the color is reversed, with red on the bottom. Credit: Leonardo Weiss via Wikimedia Commons. Sometimes you can see another, fainter secondary rainbow above the primary rainbow.
The primary rainbow is caused from one reflection inside the water droplet. This is why the secondary rainbow appears above the primary rainbow. A rainbow has seven colors because water droplets in the atmosphere break sunlight into seven colors. A prism similarly divides light into seven colors.
When light leaves one medium and enters another, the light changes its propagation direction and bends. This is called refraction. However, because of differences of refractive index, this refraction angle varies for each color or according to the wavelength of the light. This change of the angle of refraction, or refractive index, in accordance with the wavelength of light is called dispersion. In conventional media, the shorter the wavelength or the bluer the light , the larger the refractive index.
The angle of refraction depends on the speed at which light travels through a medium. People have noticed the phenomenon of refraction throughout history. But the first to discover the law of refraction was Willebrord Snell , a Dutch mathematician.
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