Wednesday, June 15, 2011


Ditch the rose-colored glasses and prepare yourself for full-on Technicolor. Today on learnalittle, we’re chasing rainbows.

Rainbows appear when sunlight passes through moisture droplets in the atmosphere, producing a colorful ring – though only an arc is visible. When the sun is about 42° above the horizon (in the early morning or evening), droplets of moisture behave much like prisms: a ray of light refracts as it enters the droplet, reflects off the back, then refracts once more as it passes out of the droplet. This process disperses the ray into the colors of the visible spectrum of light.

For centuries, Isaac Newton’s seven colors of the rainbow defined this spectrum. But recently, indigo lost its status, as most people can’t distinguish it from blue or violet. Some scientists suggest cyan – easily visible between blue and green – take its place. As a side note, the last color in the rainbow is indeed violet; purple is considered a separate color between red and violet.

When light is reflected twice in one droplet, it causes a double rainbow: a fainter, second arc above the first. Whereas a primary rainbow’s top band is red, a double rainbow’s colors are inverted. The space between the two rainbows appears darker than the rest of sky, as little light escapes the droplet at this angle.

Although rare, triple rainbows do occur. However, due to their angle of reflection, third rainbows do not appear above the second, but on the opposite side of the sky. Because they’re in the direction of the sun and quite dim, triple rainbows are hard to see. For this reason, quadruple or quintuple rainbows may never be visible in nature. However, using super bright lasers, researchers have observed up to 200th-order rainbows!

Rarely, one might see supernumerary rainbows: dim, off-color additional bands stacked under the primary rainbow. Supernumerary rainbows can’t be explained by the optic geometry that demonstrates how light bounces around inside water droplets. Indeed, these mysterious pastel colored bands were key in establishing light’s particle-wave duality.

Rainbows are optical phenomena, not physical objects. When there’s a rainbow in the sky, each observer actually sees a unique image from his or her specific vantage point. For this reason, you can’t actually approach a rainbow, let alone get to the end or go over one. As you get closer, the rainbow will stay the same distance until it’s no longer visible. If someone appears to be standing at the end, it’s only the end of the rainbow you see; they’re seeing another rainbow further away.

Rainbows are powerfully symbolic, and have been adopted by various groups to represent their cause and values. In South America, the rainbow flag means Inca heritage; in Italy, it’s a symbol of peace; and it’s emblematic of the Queer Community across the world. Like real rainbows, the feelings and ideals rainbows represent are unique to each person.  No matter what they mean to you, hopefully you’ll see rainbows a little more clearly from now on.

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