17 wonderfully curious facts about rainbows

double rainbow
CC BY 1.0 Wikimedia Commons

Who knew these “rainy arches” had such a colorful history?!

It’s hard to see a rainbow and not feel like a little special something is happening. Some of us may even stop in our tracks and swoon at the beauty of the thing, not to mention become elated at the promise of good fortune to follow. Rainbows are stunning, like shooting stars and Northern lights, they are total magic, Mother Nature style. A fact not lost on just about every culture since time began.

But while we all know that a pot of gold awaits the person lucky enough to get to the end of a rainbow, what else do we really know about these candy-colored phenomena? There’s more to a rainbow than meets the eye! Consider the following:

1. “Rainbow” comes from the Latin arcus pluvius, meaning “rainy arch.”

2. In Greek and Roman times, it was believed that rainbows were a path created by the goddess of the rainbow, Iris, linking us to the immortals.

3. What do rainbows have to so with peacocks? The Greeks used the word “iris” to refer to any colored circle, thus the iris of the eye or even the spot on the tail of a peacock. Other words that take their cue from the goddess of the rainbow include the iris flower, the chemical iridium, and the word “iridescent.”

4. Even though rainbows figure prominently in the myths and religions of so many cultures throughout history, no one had any idea what the heck they actually were until the 17th century.

5. The Greek epic poet Homer believed that rainbows were made of a single color, purple. (How decidedly unpoetic.)

6. The Greek philosopher Xenophanes elaborated by bestowing the rainbow with another two colors, saying that it was comprised of purple, yellow-green, and red.

rainbowWikimedia Commons/CC BY 2.0

7. Aristotle agreed with Xenophanes in his treatise, Meteorologica: “The rainbow has three colors, and these three, and no others.” Apparently this was a hot topic!

8. During the Renaissance, it was decided that, no, there were four colors: red, blue, green, and yellow. By the 17th century, western thinkers had agreed upon five colors: red, yellow, green, blue, and purple.

9. In 1637 René Descartes discovered that rainbows were caused by light from the sun being split into different colors by rain. Gold star for Descartes.

10. In 1666, Isaac Newton added indigo and orange to give us the seven-colored Roy G. Biv that we all know and love today. However, in China rainbows are considerer to contain just five colors.

11. The truth is, there is no set number of colors in a rainbow! Each hue blends into the next without a hard boundary, leaving the interpretation up to the person who sees it and the culture that has defined it. (I'm going with 28 colors, so there.)

12. And in fact, a rainbow doesn’t even actually “exist,” … it’s not an object, it’s an optical phenomenon. Which is why no two people see the same rainbow.

13. The Telegraph explains the magic as such: "Each raindrop acts as a tiny, imperfect mirror. When the sun is right behind you its light passes through the raindrops in front of you, reflects off their rear surface and bounces back at you. The light is refracted or “bent” slightly as it passes from the air into the water; and again as it bounces back into the air again. The different wavelengths that combine to make daylight are “bent” by different amounts (42º for the red end of the spectrum, a shade less for the violet). Each raindrop acts as both prism (refraction) and mirror (reflection)."

14. Double rainbows occur when light bounces inside the water droplet more than once before escaping, the spectrum of the second arch will be reversed. Sometimes third or fourth rainbows can be seen.

15. Between a rainbow and its double the sky is darker because light reflected in raindrops in this part does not reach the observer. Word nerd alert! This area has a name: an Alexander's band, named after Alexander of Aphrodisias who first described it in 200 AD.

16. Rainbows can occur in mist, fog, sea spray, waterfalls and anywhere where light meets water in the sky and the angles are conducive. There are also rare moonbows, made at night by the light of the moon … though our eyes read these as white. This is a very good time to look for unicorns.

17. The world’s longest-lasting (or longest-observed) rainbow was seen over Sheffield, England on March 14, 1994 – it lasted from 9am to 3pm. (If there were ever an opportunity to secure a pot of gold...!)

Bonus! The number one rainbow-related video on YouTube, with a current 188,074,716 views, belongs to Israel "IZ" Kamakawiwoʻole's ukulele-fueled rendition of "Over the Rainbow." But since I'm old-school, here's Judy Garland and Toto instead.

(Sources: The Telegraph, Center for Science Education.)

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