Who doesn't like rainbows? Sure, some grouches might not care too much for them. But watch what happens when a rainbow suddenly, almost magically, appears on the horizon, a delicate burst of color gently washed across the sky. People stop what they're doing. Stare. Snap photos with their iPhones. And smile.
A rainbow's ability to bring joy to just about anyone is probably why they're painted on kids' cheeks at fairs. Why they're used to decorate birthday cakes, garden flags and bedding. Why they're mentioned in lyrics, poems and other writings. Why they're the stuff of folklore across many countries and peoples, often signifying a link to God or the heavens.
So what, exactly, is a rainbow? Strangely, it's just an optical illusion. We see rainbows when light strikes drops of water. The light is refracted, or changes directions, then is reflected by the back of the water drops. As this reflected light is leaving the water, it's refracted again at several angles [source: National Geographic].
You'd think we mortals would know everything about rainbows, as popular as they are. Yet there are actually quite a few myths out there about these multihued illusions. Think you're pretty rainbow-savvy? Here's betting you learn at least one new fact about them by the time you finish this article. Our first rainbow myth is probably the most famous.
One of the most storied rainbow myths is that there's a pot of gold at the end of every one. Not only that, but that the pot of gold is guarded by a tricky leprechaun. The legend goes like this:
Once upon a time, the Vikings lived in Ireland, looting and plundering as they pleased, then burying their ill-gotten treasures all over the countryside. When they eventually departed from the Emerald Isle, they inadvertently left behind some of their booty, which the leprechauns found. Now, the leprechauns knew the Vikings had gotten their treasures through stealing, which was wrong. This bad behavior made the leprechauns mistrust all people, Viking or not. In order to ensure no humans could take what they now considered their gold, the leprechauns reburied it in pots deep underground all over the island. When rainbows appear, they always end at a spot where some leprechaun's pot of gold is buried [source: Mystical Myth].
Here's the catch: Believers who've searched for the legendary pot o' gold always end up stymied, because they can never find the rainbow's end. The reason for that is on the next page.
It's true rainbows appear to form perfectly rounded arches. But in reality, rainbows form full circles. Then why don't we see circles? When we're standing on the ground, we can only see light that's reflected by raindrops above the horizon. Thus, we can't see a rainbow's lower, hidden half. There is one way you may be able to see a full-circle rainbow, though. If you're a pilot or passenger in an airplane or helicopter – and thus can see below the horizon – you might see a rainbow as a full circle. Sometimes people climbing tall mountains can view circular rainbows as well [sources: Lewin, National Geographic].
Since a rainbow is a circle you'll never reach the end or the bottom. Rainbows seem to move when you do, because the light that forms the bow is always at a specific distance and angle from you [source: Howard]. Remember we said earlier that rainbows were optical illusions? That's why you'll never find your pot of gold, alas.
This is an interesting "myth," because depending on how you look at it, it can be considered a true or false statement. In school you probably learned that the colors of the rainbow are (in order) red, orange, yellow, green, blue, indigo and violet. These are actually the colors of the visible spectrum. Red has the longest wavelength and violet the shortest. (Some scientists think indigo is so similar to blue that it's indistinguishable for most people [source: National Geographic].) But those seven hues are not the only ones in the world, of course. Where's the pink, for example? Or brown? Or sage, aqua, celadon and coral?
Those colors, and more, are actually there in the rainbow. They're just invisible. Rainbows contain upward of 1 million colors – that's right, 1 million – in a much larger continuum than the seven measly ones with which we're familiar [source: Howard]. Unfortunately, our human peepers can't see all of those other hues. So does this mean rainbows contain them or not? That's for you to debate.
One of the more fascinating facts about rainbows is that no two people can see the exact same rainbow. You may think you're seeing the same thing; you might even describe the rainbow you're seeing to the friend next to you, who will agree that what she's seeing looks just like the one you described. But you're truly not seeing the same thing. Here's why:
When you're looking at a rainbow, you're looking at light that's reflected by raindrops sitting above the horizon. But your horizon is always different – albeit, sometimes only slightly different – from everyone else's, and vice versa. To put it a little differently, the center of the rainbow arc you're seeing sits on an imaginary line stretching from your eye to the sun. Since your eyes and those of someone else's, even someone next to you, can't be in the same place in space simultaneously, the two of you can never see the same rainbow. If that's not enough to ponder, consider this: Even our own two eyes see slightly different rainbows [sources: National Geographic, Rao, Science Kids].
This seems to make sense – there's that word "rain" in "rainbow" after all. And with good reason. For a rainbow to be formed, there need to be water droplets in the air. Then, light has to shine through those droplets at just the right angle. If this happens – voilà! A rainbow!
But water droplets can be in the air for many other reasons. When it's misty outside or when there's overspray from, say, a waterfall or waves crashing against rocks; in foggy weather; around a fountain or even when it's dewy out. No matter what the source of the water droplets in the air, though, remember that the sun has to be at the proper angle – no higher than about 42 degrees of altitude – or the rainbow will be below the horizon and you most likely won't see it. If everything is in place, you still have to have the sunlight at your back in order to see the rainbow [sources: Edens, Rao].
We've been talking about how water and sunlight are the ingredients for a rainbow. If this is the case, then it should follow that rainbows can only pop out during the day. But they can actually occur at night, too. An evening rainbow is called a moonbow, or lunar rainbow. Moonbows are created when light reflected by the moon hits water droplets in the air. Before you think a moonbow can't be a rainbow if it's made from water and moonlight (not sunlight), remember that moonlight is actually reflected sunlight; the moon doesn't give off any light [source: National Geographic].
For a moonbow to form there needs to be a full or nearly full moon. And, as we said earlier, some water in the air. Because tropical areas such as the Caribbean and Hawaii tend to have showers lasting well into the evening, moonbows most frequently appear in these locales. All of the same colors in a rainbow are present in a moonbow. But moonbows are pretty faint, since moonlight is so much dimmer than sunshine. Since our eyes can't perceive colors when the lighting is dim, we see moonbows as white. Interestingly, though, photos of moonbows do show their colors [sources: Live Science, National Geographic, Science Kids].
Oh yes you can! You may have already done so as a kid and just forgot. All you need to do is turn on a garden hose, stand with your back to the sun, then adjust the hose's nozzle so the water comes out in a fine spray. Look closely – a rainbow will appear in the spray [source: Rao].
If you'd rather create a rainbow via a more official science experiment, gather a shallow pan, water, white paper and mirror. Fill the pan half-full with water, then set the mirror in the pan at an angle. Head outside (it has to be a sunny day) and adjust the pan so that the sunlight hits the portion of the mirror that's submerged in the water. Take your white piece of paper and hold it above the mirror, moving it to different angles until, magically, a rainbow appears on the paper. Only cloudy skies in your neck of the woods? Use a flashlight to replace the sun [source: Merali].
Not only can you create rainbows, you can make them disappear too! And it doesn't involve something like chanting, "Rain, rain, go away. Come again another day!" All you have to do is grab a pair of polarized sunglasses, hold them in front of you vertically, and – poof – no more rainbow. What's going on?
Rainbows are highly polarized objects, which basically means their light waves are vibrating in one plane – in this case, a vertical one. Sunglasses are also polarized vertically. This is because they're created to block reflections and glare, which typically come off of pools of water and other flat surfaces, and are polarized horizontally. Horizontal light waves can't get through vertical polarizers. Thus, if you're wearing vertically polarized sunglasses, you can see vertically polarized rainbows. But turn those sunglasses on their side, effectively creating a horizontally polarized set of shades, and the rainbow's light waves will be blocked, causing the rainbow to mysteriously disappear [sources: Plait, Polarization].
You might think that your chances of seeing a rainbow have nothing to do with the time of day. After all, there can be rain, fog or mist followed by a burst of sunshine in the morning, noon or as evening approaches. This is true, yet showers (one of the most common rainbow precursors) are much more frequent in the late afternoon than they are in the early morning or midday, so rainbow sightings are more likely as the day is winding down. The sun is also at a more favorable angle then – 42 degrees or lower in the horizon [sources: Howard, Rao].
We should mention that this phenomenon mainly pertains to rainbows and the summer. In cooler months when the sun doesn't get as high, you might well see a rainbow in midday [source: KOMO News].
Storms typically move from the west to the east, while the sun rises in the east and sets in the west. So if it's raining in the morning, it will likely be raining in the west. Since the sun is in the east, any visible rainbows will be in the west (the sun has to be at your back in order to see a rainbow). In the late afternoon, the situation will be reversed. Now the sun is in the west, and any showers that pop up will hit your locale, then move to the east – the direction you'll need to be looking (with the sun at your back) if you want to spot a rainbow [source: Rao].
Rainbows can multiply. Double, tertiary (triple) and quaternary (quadruple) rainbows all can occur. Double rainbows occur when light gets reflected twice inside water droplets. When this happens, the second rainbow appears above the main one and is fainter. Its colors are also reversed (red is on the inner section and violet on the outer arch) due to the second reflection [source: National Geographic].
A tertiary rainbow occurs when light is reflected a third time. But you have to be facing the sun to see one because the sun is its center. Tertiary rainbows are very difficult to notice partly because you're looking into the sun, and partly because they're quite faint and very broad. Even harder to see are quaternary rainbows, which form when light is reflected a fourth time. You also need to be facing the sun to spot these, and they're even fainter than tertiary rainbows [source: National Geographic].
And it doesn't stop there: Scientists have detected a 200th order rainbow (that's a rainbow with light reflected 200 times) in the lab!
So now it's time to confess. Were you stumped by any of these? If you weren't, I'd suggest investigating a career in meteorology.
HowStuffWorks takes a look at the phenomenon of noctilucent clouds and how they are formed.
Author's Note: 10 Myths About Rainbows
I definitely learned a thing or two (or three or four) from researching this article. Now I'm on a mission to spot a moonbow. Guess that means I need to go to the Caribbean ...
More Great Links
- Colours of the Rainbow. "Rainbow Legends." (Feb. 23, 2015) http://www.colours-of-the-rainbow.com/legends.html
- Edens, Harald. "Frequently asked questions about the rainbow." Weatherscapes. (Feb. 27, 2015) http://www.weatherscapes.com/techniques.php?cat=optics&page=rainbowfaq
- Howard, Jacqueline. "Two People Never See The Same Rainbow – And 6 More Amazing Facts About The Optical Phenomenon." The Huffington Post. Aug. 31, 2013. (Feb. 24, 2015) http://www.huffingtonpost.com/2013/08/31/facts-about-rainbows_n_3779801.html
- Lewin, Adrienne Mand. "7 colorful facts you didn't know about rainbows." Today. June 21, 2012. (Feb. 25, 2015) http://www.today.com/id/47891913/ns/today-weather/t/colorful-facts-you-didnt-know-about-rainbows/#.VO6NeyyGNCA
- Mahlen, Gena. "How a Rainbow is Formed." (Feb. 27, 2015) http://faculty.cord.edu/manning/physics215/studentpages/genamahlen.html
- Merali, Aliya. "Create Your Own Rainbow." Physics Central. (March 1, 2015) http://physicscentral.com/experiment/physicsathome/rainbow.cfm
- Mystical Myth. "Irish Pot of Gold." (Feb. 26, 2015) http://www.bellaterreno.com/art/irish/irish_potgold.aspx
- National Geographic. "Rainbow." (Feb. 23, 2015) http://education.nationalgeographic.com/education/encyclopedia/rainbow/?ar_a=1
- Plait, Phil. "Polarized rainbow, what does this mean???" Discover Magazine. Aug. 18, 2011. (March 1, 2015) http://blogs.discovermagazine.com/badastronomy/2011/08/18/polarized-rainbow-what-does-this-mean/#.VPMpVi6wjfY
- Polarization. Rainbow. "A Polarized Arch? Halos? Glories?" (March 1, 2015) https://www.polarization.com/rainbow/rainbow.html
- Rao, Joe. "Rainbows: How They Form & How to See Them. Live Science." March 15, 2011. (Feb. 27, 2015) http://www.livescience.com/30235-rainbows-formation-explainer.html
- Science Kids. "Rainbow Facts For Kids." (Feb. 23, 2015) http://www.sciencekids.co.nz/sciencefacts/weather/rainbows.html
- Your Irish. "The Magical Legend Of The Leprechaun." (Feb. 26, 2015) http://www.yourirish.com/folklore/the-leprechauns/