Rainbows: Delighting humanity since forever

on the podcast before. I am sure that you have. So how are you doing? I'm great man, rainbows, As the author points out, they've inspired countless fairytale songs and legends. Man, I love rainbows. I think rainbows are just fantastic. They're probably the greatest graphic design of all time. I just think rainbows are great. Well, it is funny too when you read the different articles how people it's kind of corny when they talk about how they delight and astound.

But darn it, when you see a rainbow, even as a jaded, cynical adult, I can I there's no way you can't look and just go, oh, that's pretty neat. Yeah, at the very least you'll go, oh, a rainbow. If somebody says, hey, there's a rainbow over there, you're going to look up. I don't care. And if you doubt, if you doubt a rainbow's ability to astound adults, all you have to do is look up Yosemite Bears double Rainbow video, which I watched today. It's pretty pretty great stuff.

All bear vesque is what does it mean? I know what it means. You're on pot. You know. Next time someone does to see a rainbow and say that, I'm gonna test everything and just say so now I'm gonna look, all right, Let's see if they just think I'm dead inside. Let's see what happens. I'm curious to see whether you can not look. Of course I look, um, so chuck that we're not the first to be delighted and amused by rainbows. Several years, decades at least, they've been around forever.

There there is a lot of mythology surrounding them, because you know, they're unusual. They don't happen every day, and well, I guess they depends on where you live, but it's not necessarily in a normal occurrence. No, I found that um. The philosopher Descartes renee Decarte was the first to describe kind of the modern accurate theory in six seven. Oh yeah, he's the first one. It's like, hey, wait a minute, there's some refraction and going on here, right, Well, most

people usually associate that with Newton. Yeah, well he's the first one to describe the spectrum, right he was. And apparently I saw this cool video by Philip Ball on the Atlantic Um that basically said that Newton just made up the roy G biv um spectrum. What do you mean? So the the red, orange, yellow, green, blue, indigo, violet

is Newton's interpretation of the rainbow. Before that, all sorts of different cultures had different ideas of what made up a rainbow, how many colors there were, what the colors were, um, and our interpretation of the rainbow spectrum is a Newtonian invention. And a lot of people say it's not seven, it's actually six indigo, not really bare Newton. And apparently Newton was trying to shoehorn the rainbow spectrum into the musical octave.

So he's he tried. He's trying to shoehorn music which has sound wavelengths with light which has wavelengths and making them one and the same. But history has kind of shown like, non, there's six, we'll go with six for the rainbow. So roy G BIV, which we learned in school. Apparently I learned school. You did too, it's just roy g h. Yeah. Well he was busy making is uh cookies from figs too, so he had lots of stuff going on. Those are good. Oh yeah, I can mount

some pig nets. Yeah, because they're good for you, so you can eat the whole bag one sitting if you want. Yeah. I'd never buy them, but um, if I see them on like if you give blood or something, they're on a snack table, that's when I get my fig Newton on. Yeah. So, um, Newton wasn't the only one. Before Newton, there was like a whole Celtic legend about the pot of gold at

the end of the rainbow. There was God saying more bad after the Great flood and promising it would never happen again by showing rainbows come out after rains like it's fine, it's stopping, We're not going to flood the earth again. Um. Of course you can't find a pot of goal at the end of the rainbow because you cannot go to the end of a rainbow. Yes, you never. You can't go under a rainbow. You can't go over

a rainbow. And we'll explain all this why, Yeah, and just a second, sure, but first we have to talk about to get to the bottom of how rainbows work, which to me I think is awesome. It's one of those things where okay, this is how it works, we understand it now. Yeah. I love science stuff like that, um baked in science. Yes, just done. It's not like scientists think this is what's happening, and that's probably true,

but that remains to be seen. This is one of those ones where like, we know how rainbows work and here's how. But to get to the bottom of rainbows, we have to understand how light works first. Yeah, and I thought this article, even though there was a lot more digging in to do, I thought the shopping cart explanation for for basically how light travels was pretty pretty darn good, fantastic. You know, one reason they say visible spectrum is because the light is moving so fast that

you can't see it. It's like in the combination of all those is is white light like the sun is white light because all those colors are superimposed on one another. But when it hits like a water droplet or something else, it's gonna slow down enough. And we'll get to all this to where you can see those individual parts of the spectrum, right, and and that that shopping cart explanation, like you said, it definitely simplifies the whole thing, and it's not quite right, but it does a pretty good

job of illustrating the principles that are going on. You know. Yeah, So basically light is moving at different speeds depending on what kind of medium, uh, it's traveling through. So, like I said, when it hits water, it's gonna slow down a lot. That's gonna change its speed. If you're pushing a shopping cart, the asphalt is the medium. If you push it onto grass, it's gonna slow down. That's a new medium. It's a new medium. It's gone. It's transition

from one media to another. That's right. And if you hit that grass at an angle, and we've probably done this. If you had a were able to steal a shopping cart as a kid, you're pushing your friends around in it,

you're hauling through the neighborhood. And you hit that grass at an angle, and it's gonna take a really sharp turn because that front right wheel, let's say, is going to hit the grass and all of a sudden, really quickly, it's gonna be traveling at a much slower speed than the rest of it, and your friends gonna tumble out and everyone's gonna have a good time exactly just where your helmet. So so that imagine that the shopping cart is a photon of light or a beam of white

visible sunlight, and the grass is a prism. Yeah. So the parking lot was air and it was moving through just find no problem. But when it hit that prism, it slowed down. And because it came at an angle, one side of the light hit sooner and it made it turn. And that it's called refraction. The bending of light is refraction. Yeah. And in the case of a rainbow, that prism is a rain drop. So I mean this

is the simple quick version. We'll get more detailed. But when it hits that raindrop, it's gonna slow down and it's gonna bend. Right. So depending on the um refractive index, which is how much light bends depending on the wavelength um, the the wavelength of light, which is another term for color,

is going to bend at a different angle. So when that visible light, which is all the colors of of the visible spectrum combined, hits a prism and it bends or a rain drop, right, it bends at different angles because the wavelengths are different, and so that visible light comes undone into its component wavelengths, which are all the

colors of the rainbow, and they spread out. It's called dispersion, right, yeah, and that's it really, But like I said, in this case, we're talking about rain uh and because rain is um you know, raindrops are all different shapes and sizes, it's not gonna be as consistent as like a prism might be,

but it's gonna have the same effect. It's gonna hit hit the rain drop, it's gonna slow down like the field digging into the grass of the shopping cart, and it's going to refract and some of it's gonna keep going someone it's gonna bounce back, but different the different color is going to bounce at a different angle, and it's all relative to where you are on the ground. Like, no person two people see the same rainbow. Right, So, um,

when Abe right. So when when light hits the prism and it bends, like you said, because the different lights have different wavelengths. Different colors have different wavelengths. Um red has the longest wavelength, so it bends the least. I believe violet has the u shortest wavelength, so it bends the most. But because again because these different wavelengths, they bend differently, so that the light spreads apart, and when it exits the prism, it bends again and it forms

that spectrum of separated light separated out. And this, if you notice we keep saying the had been that's why a rainbow is an arc instead of like a right angle, because the light is bending. So Chuck, we've been kind of teasing this a little bit. But um, we'll get into exactly how you go from prison to rain drop and hence the rainbow right after this. All right, if you want to see a rainbow, or if you're gonna

see a rainbow, there need to be three conditions. Uh, the sun's got to be behind you, You're gonna have moisture in front of you, and you the sun must be shining. That sun, those sun's rays must be shining at forty two degrees of what's called the anti solar point, which is basically where the shadow of your head is on the ground. So if you can see the shadow of your head, that's that's going to be that forty

two degree anti solar point. So what you do is you put your back directly to the sun right and then turn forty two degrees, which I guess if it were negative forty two degrees, you'll be turning to the left. So I guess you'd be turning to the right a little bit about forty two degrees, which you can kind of measure off in your head. It's not quite forty

five degrees. And if you're looking at rain and the sun is behind you, you're gonna see where that forty two agrees is, because once you hit that point, there's your rainbow. Yeah, but I mean you can move your body around and still see the rainbow. I mean that's where the sun is hitting. The Sun's got to be hitting at forty two degrees. I see. Okay, so Chuck, it doesn't matter then where your head is. It's it's the rain drops relation to the sun needs to be

forty two degrees. The producer rainbow. Yeah, the sunshine must be hitting it at forty two degrees. Okay, so let's let's get back to basics again for a second. Um. When the sunlight hits the rain drop, each individual raindrop is acting like a prism, right, So that visible white light is hitting a raindrop, it's hitting it at an angle.

It's going kaboom into like a colored spectrum inside the raindrop, and then it's gonna reflect back again, refract again, exiting the raindrop, so it bends again and it comes back at you. The thing is is when you see light colored light wavelength from a rain drop, you're not seeing the whole spectrum. You're not seeing millions of little rainbows.

You're seeing one big rainbow. And the reason why is because each individual raindrop, depending on its relation to you and I guess to the sun, is shooting one color at you. It's shooting all colors at you, but you're only picking up on one color because there's only one color from a rain drop that is angled correctly to you and your line of sight, so that it's the only one you're picking up on, his red. And then all of the rain drops around that rain drop are

doing the same thing. They're shooting about in relation to your line of sight red towards you. But then the rain drops a little lower than that are shooting yellow, and then lower than that green, and so on and so on, and so you get the violet. And so these groups of rain these groups of rain drops are producing this rainbow cumulatively as far as your line of sight is concerned. Yeah, because the rain is just falling, so where it is in the sky, I mean, as

it falls, it's going to be changing color. You know, it's not like frozen in midair or anything, but it seems like it. But it seems like it, right exactly. And't that phenomenal? It really is. I just think that's just as cool as it gets. Yeah, it's super cool. And um, you'll always notice to the sky under the rainbow is going to be brighter than out. And when you've got a double rainbow, which we'll get to the the area between those two is usually really dark, right,

And that's called the Alexander's Dark Band. Yeah, Alexander's Band because he was Alexander Frio. Aphrodiseus was the first dude to describe that. That's a great name, Alexander Aphrodiseus. Yeah, it's pretty good. It sounds like a seventies exploitation movie or something. Um. But yeah, So the reason why in between the double rainbows you have Alexander's band is because the light there is reflecting away from you and it's

so it's a dark area. So, uh, the sunlight hitting those rain drops is going away and you're like, oh, it's dark inside the rainbow. All of that light is reflecting back to you and you're seeing all of the different colors come at you and they're recombining indivisible lights, so there's no color, it's just bright sunlight in the middle. Yeah, and that you know sunlight. They also always describe it as white, I mean sunlight as all the colors. We

just you know, can't see it. Yeah, we should really do a whole um How Color Works episode. It's fascinating stuff. But yeah, depending on whether you're a painter, um who's mixing chemical color, whether you're a chemist or a physicist, white is either the presence of all colors or the absence of color. You know, it's kind of mind blowing. We should totally do how color works. Uh. Well, I guess after this break we'll talk a little bit more about the double rainbow all the way and even well,

well we'll just leave it at that. What does it mean, so, Chuck, you want to talk about double rainbows and what forms them, it's pretty much the same thing, right, Yeah, the lights refracted twice. Yeah, it's just a double refraction. Yeah. Well, what's cool is if you look at a double rainbow, the one on top, the higher one, that's the second refraction, um is reversed, so rather than red being on the top, it's on the bottom. Yeah, it's the reverse rainbow. Is

what a double rainbow is. And you can have a triple and even a quad, but it's rare, Like I've seen a little bit of a triple once. I think, um to where you just see the faintest hint of that third one, And if you're seeing that, that means the initially I think it's called the primary and secondary.

That means your primary is super super super sharp. Yeah, to where it looks like it's drawn on the sky, painted on the sky, and then your secondary is gonna be a little more faint than the third one because the triple refraction, you know, it's it's not the easiest

thing to occur in nature. Yeah, and one of the things that makes the primary rainbow and then hence the secondary and I guess herst ayan so on rainbows bright is the amount of sunlight and the number of raindrops, because remember those raindrops that you're seeing, that the spectrum is made up of light wavelengths that's coming at you from a bunch of different raindrops, and they reinforce one another, and the more they reinforce one another, the brighter the

rainbow is. Yeah, And you know, I mean I feel like I usually see rainbows when it's not raining where I'm standing, but um, that doesn't matter. It's you know, you can be being rained on and still see the rainbow. Well yeah, but it's like sometimes it's like a super light rain where it has just rain really hard. Maybe it's tapering off or maybe stopped all together. But the point is where the rainbow is. It's it's not like they said earlier, you can't drive up to a rainbow.

I'm gonna go up and find that thing because it's a it's just a perspective trick basically, right. The only apparently from this Scientific American article you sent, the only visual information we get from a rainbow is the band of its arc. Yeah, and everything else is what's around it, right, right, So, like, if a rainbow seems really huge, it's because, say, the mountains in the background looks small, which makes the rainbow,

by contrast, look very big and majestic. If we're close to, say, like the mountains are like a cell phone tower or something like that, the rainbow may look very small by comparison. Yeah, and the way they like in it, and that I think, um, and that article I think was like the human head. It's like roughly the same size, but if it was right in front of your face, it would block out a whole movie screen. But it was further way, it would just be like, hey, and there's that guy's head.

It's the same thing, same thing. Um. And then Phil Plate, who is a who does the Bad astronomer Um blog for Slate, he did a pretty good explanation of um full circle rainbows. Yeah, I had never ever heard of that until you sent me that, so it makes sense though, it totally does. So. Remember we talked about a rainbow arching over the sky and because the light is bent out of the prism, Well, no, it's because it starts on one part of the ground. And ends on another

part where the goal is. Um. The reason why it has that arc is because what you're seeing is part of what really is a full circle, and it's depending on where you are. Now, you have a certain amount of raindrops available for to reflect the light to you. Right, So when you're on the ground and you're looking up or just over to the horizon, you have a certain amount of raindrops available to you to form a rainbow.

If you were able to get away from the ground, you have even more raindrops that's just above you, but now below you as well, and you can see a full circle. That is the actual real rainbow. Yeah. So a real a real rainbow, depending on where you are in relation to the ground, is either a part of a circle, an arc, or a full circle. Yeah. And there was a picture. I mean he said that pilots see him all the time or I guess if you're an astute flyer, that's not just like asleep with a

black blanket of your face. Right. Um, you can look out a window of a plane and see one two because you're above it. It's pretty neat. I mean, there was a photo of one and it was like, oh wow, there's a full circle rainbow, full circle rainbow. It looks it looks kind of like a lens flare a little bit, but it's a rainbow lens flare. And um, phil Plate had in that same blog post a double circle rainbow, which was really neat. Yea, so go check that out.

I agree that was pretty cool. Um. Yeah, you know that thing we're talking about earlier to about the perspective. That's why the I think I thought you did it. Don't be dumb about why the moon looks bigger? Have you done that? No? It's so why can you see the moon during the day sometimes? Why is that? Well I'll tell you why, because I saw it like a one the other day that was like super late in the day. Well, the reason why, A better question is why can't you see the moon all the time, even

during the day. So it's not the moon is very bright, it's it's the brightest object in the sky, second only to the sun. Sure, but it also gets its light from the sun. So most of the time when you can't see the moon during the day, it's because the moon is behind you. So the light that it's getting from the sun is behind you. Now, if the moon is closer to the Sun. Like depending on where the moon is in its lunar phase, then you can look up and see the Sun and the Moon at the

same time. It's above the horizon. In other words, so if you if the moon were always visible above the horizon, you'd always be able to see it during the day. And it just has to do with where it is in relation to the Sun in the lunar phase. Does that make sense? Yeah, if if if it's man, just go watch that. Don't be dumb on it. Yeah. They

call that a bonus, an impromptu bonus. But the reason why the moon will look really huge in the sky is because the same thing we're talking about with the perspective like the mountains, is like when you're low on the horizon, it's gonna look enormous. Um if there's a lot less stuff. Yeah, and near close to you, it's gonna look very big. Yeah. And when I went to Montana years ago, my explanation I got because you step off the plane and you think, wow, this sky does

look bigger, Like what's the deal? They call it big Sky Country and it really does look bigger. And the explation I got from the locals, what's it's because the clouds. So again it's just a perspective trick. So like the mountains are way over there. I think it's just the clouds that they typically out of, the big, huge puffy clouds and um, but they look big in relation to the mountains in the distance. Yeah, I think that's the deal.

So it makes the sky appear to look larger. Plus I I imagine also there's fewer obstacles and obstructions, so that it's just there's more sky to see and take in just looking around, right, Yeah. Yeah, Like when I lived in Yuma and you go out in the desert and you can see like a hundred and eight degrees from horizon to horizon, um, but they don't have the

cloud formations. Um. So the sky looks bigger in Montana than it does like in the middle of the desert, because most of the time in the desert you're going to see that, you know, just blue, nothing but blue. So there's no perspective, you know, like when you take a picture of something to sell on eBay, you put your fists next to it so people know how big it is. Is that what people do? Any seeing quarters and rulers never seen this, Yeah, that's quarters and rulers.

That's probably a better rule of them, right Yeah. Um, so, Chuck, I got a couple other things. Apparently, when you look at a rainbow, it's not uh an even division or an even representation of all the colors. Um you see the most red, it's the most visible. Apparently thirty eight percent of a rainbow is red. Green is second at fifteen. Blue is the least um with just eleven percent. What

is green? Green? Is? Okay? Rainbow green? Interesting? I wonder what color blind We need to do one on color blindness, but it's um. I looked into the article and it was just sort of started to melt my brain, like all this stuff, so I just said, no, put that on the back burner. I think you did a great job with this. Well we'll see, I'm sure we'll get

stuff wrong. H And lastly, the LGBT rainbow flag designed in by a guy named Gilbert Baker really and it used to have eight had turquoise and hot pink on it before um, but apparently they ran out of fabric for hot pink because the things like started to take off, so they discontinued that. And I think the same went

for the turquoise one too interesting. We just went with six and now is it a is it's a It's a shining monument for establishments, for people to say I want to go in there, and some people to say I don't want to go in there. Sadly. You know. We went to a gay bar in Philadelphia one afternoon, um, and I say by accident, not like it was a big deal. Was it the Blue Oyster? Now? And it was in the afternoon, so it was just you know, you know how it is in some bars in the afternoon,

like the that the serious regulars are in there. It doesn't matter, gay, straight, whatever. And they were very cool guys, and they were like, uh, and it was a big group of us, and I think they were like, you know, you know you're in a gay bar, right, And they were kind of pointing that out. And I was like, oh, well, great, serve me, bloody Mary. Then like I didn't know if he thought we were I think he knew here from out of town, so he was yeah, yeah, like, uh,

he didn't want any trouble. Oh got you. You know. I was like, We're not like that, my friend. That's just a happy accident. It does a good ending to the Rainbow episode. Uh. If you want to know more about rainbows, go check out our article on the site Rainbows. Just type that word into how stuff works. Go check out that Slate post and Scientific American in the Atlantic. Some good stuff out there. Uh. And I said a search bar, I think, and they're somewhere, which means it's

time for listener mail. That's right. I'm gonna call this, uh Pliny the Beer. Uh. And this is from Corey and I think Corries in San Francisco. Hey, guys, love the podcast. I was listening to Cinnamon today and there was an exchange about Pliny in a comment that there was one and only I think anyone in the Bay Area would know that there are two Plenties, the Elder

and the Younger. Um. That's because one of our local breweries has a beer called Plenty the Elder, which is known by beer officionados as one of the best beers out there. In fact, it sells out weekly from local groceries. They also make though a Plenty of the Younger, which only comes out for two weeks a year. People wait in line for hours just to get a pint. Uh. And there was also a real historical Plenty the Elder

and Plenty the Younger who is his nephew. I didn't realize it, and that is from Corey, and I did look it up because the two weeks thing, I did not believe it, but I just you know, sometimes you want to see it with your own eyes. And uh, yeah, Plenty of the Younger is a triple I p a. Oh wow, that sounds awesome, named for the nephew and adopted son evidently, and uh it is pub draft only.

They don't even bottle it. Very limited distribution locally, um, and it's seasonal, so for just two weeks a year um in February at the Bay of Bengal you can get it in in a bar, I guess in San Francisco. And it is a ten point two five center wow. Yeah, as opposed to eight for the elder. Huh. And they're both I p A s Yeah, ones that the double and the triple so that yeah, and you can get the Plenty of the Elder in the bottles. It's not

quite as exclusive. We'll have to try that on our tour. Yeah, I guess only the elder and there's someone uh unless we luck out and happen to be there during that two week period. Huh. Well, now it's in February. But if there's a bar out there that maybe wanted to just say we're out, put it under the bar, save it for a month for us, we'll be there. I

don't think that's gonna happen. If you want to correct us after we get something flagrantly wrong, like we did with the whole pliny thing, you can tweet to us at s y s K podcast. You can post it on Facebook dot com, slash stuff you Should Know. You can send us an email to Stuff Podcast at how stuff Works dot com, and, as always, join us at our home on the web, Stuff you Should Know dot com. For more on this and thousands of other topics, is it how stuff Works dot com