Rainbows: Delighting humanity since forever

Rainbows seem to defy nature, but they're really pretty simple when it comes down to it. Turns out it's just light reacting to water droplets in the air. But they sure do look cool. Learn all about how rainbows are formed in today's episode.

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Episode Transcript

Speaker 1 (00:01):
Welcome to you stuff you should know from house stuff
Works dot com. Hey, and welcome to the podcast. I'm
Josh Clark with Charles W. Chuck Bryant and Jerry Rowland.
Have we ever said Jerry's last night? I don't think so.
Well we have now it's out there. It's on the internet.

(00:22):
Even someone really updated our Wikipedia page if you look lately.
It's robust that even says, uh, their producer Jerry Jerome Rowland.
How did they know that? I guess I've said it
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,

(00:46):
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

(01:10):
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.

(01:32):
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

(01:54):
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

(02:16):
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

(02:38):
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?

(02:59):
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.

(03:22):
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

(03:45):
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

(04:07):
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

(04:30):
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.

(04:52):
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

(05:15):
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

(05:35):
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.

(05:58):
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,

(06:20):
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

(06:41):
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

(07:02):
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

(07:26):
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

(07:49):
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,

(08:11):
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

(08:33):
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,

(08:53):
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,

(09:16):
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

(09:41):
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,

(10:05):
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

(10:37):
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,

(10:58):
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.

(11:20):
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

(11:41):
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

(12:04):
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,

(12:25):
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.

(12:46):
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

(13:08):
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,

(13:29):
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,

(13:49):
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

(14:10):
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

(14:34):
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,

(14:55):
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

(15:15):
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.

(15:37):
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,

(16:10):
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,

(16:33):
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.

(16:56):
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

(17:16):
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

(17:37):
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

(18:00):
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,

(18:23):
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,

(18:43):
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

(19:03):
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

(19:24):
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,

(19:46):
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

(20:08):
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

(20:29):
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,

(20:51):
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

(21:14):
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

(21:34):
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

(21:54):
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

(22:19):
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

(22:41):
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

(23:02):
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

(23:24):
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

(23:44):
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

(24:09):
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

(24:30):
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

(24:51):
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

(25:12):
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

(25:36):
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,

(25:57):
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

(26:19):
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,

(26:39):
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

(27:00):
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

(27:21):
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.

(27:43):
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.

(28:06):
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,

(28:28):
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

(28:51):
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.

(29:13):
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