Rainbows

Physicists and philosophers from Aristotle to René Descartes to Isaac Newton developed theories around rainbows. The rainy-day phenomenon helped Arab mathematician Ibn al-Haytham, the father of modern optics and inventor of the camera obscura, better understand the physical nature of light.

Artists from virtually every movement and region of the world have featured rainbows in their work. They turn up in a 13th-century Persian manuscript and within the pages of the Ottheinrich Bible, where you can find one of the Four Horsemen of the Apocalypse wielding a rainbow in his hand. They were a favorite of artists as varied as Salvador Dali, Andy Warhol, and Grandma Moses.

More recently the rainbow has had its moment in fashion, from the tie-dyed t-shirts of 1960s flower children to iconic multicolored Louis Vuitton bags of the early 2000s. The rainbow has become the adopted symbol of the LGBTQ rights movement and a sign of tolerance, diversity, and acceptance. One of the early collective viral video moments was that of Paul L. Vasquez, the “double rainbow guy,” reacting to their appearance (he passed away this weekend).

All told, it’s likely you need more rainbows in your life. And even if you’ve had one too many, there’s an infamous Snapchat filter that lets users puke rainbows. What’s on the other side?

1,000: Colors that Roman poets Ovid and Virgil considered as part of a rainbow

3: Colors that Greek philosopher Aristotle believed were in a rainbow

7: Colors in the rainbow spectrum, devised by Sir Isaac Newton, which we still use today

1,114: Colors in the Pantone color system

12: Types of rainbows

9: Hours a rainbow lasted in Taipei, Taiwan in 2017, a likely world record

8,843: Songs that contain the word “rainbow” in the Lyrics.com database

Rainbows are illusions that begin when sunlight shines on raindrops. “White” sunlight is a combination of different colors of light created by different wavelengths. If it enters the raindrop at an angle, the light bends because the water slows it down—imagine a car hitting a patch of ice at an angle, two wheels keeping traction and forcing a turn—and bends again when it bounces back off the far side of the raindrop and exits. Red light has the longest wavelength and bends at the largest angle, 42°. Violet has the shortest, so it bends the most.

That’s why the colors generally show up in the same order every time. But not all rainbows are Roy G. Biv—different atmospheric conditions can create different types of rainbows. Dramatic, eerie monochromatic red rainbows, for example, are created when the sun is very low in the sky and light has to travel further to reach the eye, meaning long-wavelength red only shines through.

Why does it form an arc? Now you have to think in three dimensions. Imagine your eye is the point of a greater-than sign and the light is the line coming in at an angle from a single raindrop: > In three dimensions, from lots of raindrops, it would look like a cone: 0> Cut a cone in half, because of the horizon, and you get an arc. (Unless you’re in a plane or balloon, in which case you could see the whole circle of the rainbow.)

“I didn’t even think twice about what the flag would be. A rainbow fit us. It is from nature. It connects us to all the colors—all the colors of sexuality, all the diversity in our community.”

—Gilbert Baker, creator of the rainbow flag, in the documentary series In the Life

Conferences—from TEDtalks to SXSW to your favorite annual meet-up with other people in your profession—are a trillion-dollar industry. And they’ve been derailed by the coronavirus. But where there’s a will, a ring light, and an Instagram account, there’s a way. In a new series, frequent Obsession writer Anne Quito dives into the ways that conferences are adapting to an online, distributed set-up. It could even help you look more alive on your next Zoom call.

762 BC: In Homer’s Iliad, Zeus sends out a rainbow as a sign of war.

350 BC: Aristotle publishes Meteorologica, which contains his theory of rainbows and color formation.

965: Arab astronomer Ibn al-Haytham, who publishes works on optics and the nature of light, is born.

1637: French mathematician René Descartes publishes the first study of rainbows in Europe.

1665: Sir Isaac Newton identifies the seven colors of a rainbow.

1794: British painter Joseph Wright creates Landscape with a Rainbow.

1802: British poet William Wordsworth writes “My Heart Leaps Up,” also known as “The Rainbow,” while staying in England’s Lake District.

1817: Augustin-Jean Fresnel presents his wave theory of light to France’s Académie des Sciences.

1838: English mathematician George Biddell Airy models the intensity of light in a rainbow using a cubic wave-front.

1978: American artist Gilbert Baker designs the rainbow flag after a request from Harvey Milk.

1992: General Mills debuts rainbow marshmallows in Lucky Charms cereal.

2007: British rock band Radiohead releases the album In Rainbows as a pay-what-you-want download.

2012: American artist Tony Tasset creates Rainbow, a public art installation, in the Sony Pictures Studio in Culver City, California.

White rainbows, or “fog bows,” occur when the sunlight shines on fog. Since fog contains much smaller water droplets than rain, the light doesn’t refract enough to reflect distinct colors.

If you need a moment of pure sentimental whimsy, watch Kermit the Frog sing “The Rainbow Connection,” the defining ballad of the bohemian fever dream that is The Muppet Movie.

MGM tasked American composer Harold Arlen and lyricist Yip Harburg to write the music for the 1938 film The Wizard of Oz, for which they were paid a sum of $25,000. Harburg, the son of Jewish immigrants, was also known for the Depression-era song, “Brother, Can You Spare a Dime.” As NPR recounts, the duo was stumped when it came time to write a ballad for lead actress Judy Garland. Arlen decided to go on a drive with his wife to Grauman’s Chinese theater on Hollywood Boulevard (pdf), during which the melody for “Over the Rainbow” came to him.

When Arlen played the melody to Harburg, the songwriter had some reservations. “I love the tune, but I can’t write it for a little girl,” Harburg told his partner (pdf). The duo called over Ira Gershwin for help, who suggested they play it with more rhythm. The end result was the song that audiences are enthralled by today.

A rainbow actually never makes an appearance in L. Frank Baum’s book The Wonderful Wizard of Oz; that was Harburg imagining where a 12-year-old girl trying to get away from her parents might run to on the arid Kansas plains. “Well, the only colorful thing in her life would have been a rainbow,” Harburg said (pdf).

Rainbows are commonly linked to two mythical creatures; leprechauns and unicorns. Leprechauns, which first appeared in Irish folklore, are small, mischievous spirits who store pots of gold at the end of rainbows. Leprechauns are depicted as tricksters who are notoriously difficult to find. Given the fact that rainbows are spherical, and in fact don’t have an end, it appears that the joke is on us.

The combination of rainbows and unicorns, first made in the Victorian era, later became a theme at Gay Pride parades all over the world. The sarcastic expression, “it’s all rainbows and unicorns,” often said during a time of misfortune, has even become its own internet meme.

In 2011, astronomers detected a “glory” on Venus, a still-mysterious rainbow-like phenomenon of concentric circles; if you’re a frequent flyer you’ve probably seen one. The Brocken spectre, a form of glory, is the subject of Coleridge’s “Constancy to an Ideal Object.” C.T.R. Wilson invented the cloud chamber to unlock the secret of the Brocken spectre (he failed, but the Nobel was his consolation prize).

The tricky thing about glories is that their light refracts at “impossible” angles that rainbow physics can’t explain. One theory is that they travel around the surface of the raindrop as a “surface wave” before returning in the exact opposite direction. Another is classical wave tunneling (pdf), where light passing the droplet creates “electromagnetic waves within the droplet. Those waves rattle around inside the droplet and eventually tunnel back out, sending light rays back in the direction from which they came.”