from coloring books to record covers
rainbows are everywhere i bet you can
even remember the colors without
thinking twice
although in real life no one really says
indigo but i guess roy
doesn't really have the same ring to it
anyone who's tried to chase one finds
out a rainbow isn't really there you
can't go over it and you can't get to
the end of it it's become this mythical
representation of the unattainable in
navajo and norwegian mythology it's a
bridge that only gods could take between
heaven and earth and for christians and
buddhists rainbows are a level of peace
and forgiveness
and in some cultures it's a really long
and colorful unicorn
of course just because a rainbow isn't
really there doesn't mean we can't
explain how it works
the better question is why is a rainbow
and that answer is 42.
let me explain a rainbow exists because
of light
water and a little bit of physics let's
start with sunlight it looks white now
to some that seems like the absence of
color but thanks to isaac newton we know
that white light is really the sum of
all visible wavelengths from short to
long and all the colors in between
it makes you wonder
if there are colors in between other
colors then how many colors is a rainbow
really made of
anyway so we've got lights and now we
need water on a rainy or misty day the
sky is filled with tiny droplets they
aren't quite as small as the droplets in
clouds though which is why we don't have
awesome looking clouds well some of you
might be saying
but joe i've seen a rainbow in a cloud
before
well that's not really a rainbow but
we'll talk about that another time those
suspended liquid prisms are surface
tension on its smallest scale and the
droplets are pulled into the shape of a
sphere
each one can catch sunlight and become
its own part of the rainbow factory
here's where we add in the physics
sunlight starts by entering a raindrop
from behind you
the light goes from one medium air into
another water and that causes it to bend
slightly thanks to a process called
refraction
different wavelengths of light bend at
different angles so this causes the
white light to separate
the bent sunlight then reflects off the
back of the raindrop and refracts again
on the way out when we measure the angle
between the light that went in and the
red light that comes out the answer is
42
degrees so how many drops does it take
to make a rainbow
well a lot because each color exits at a
different angle one raindrop will send
red light into your eye and another drop
will send violet light the same thing
happens with all the colors in between
each coming from their own droplet and
what about the shape i mean we call it a
rainbow for a reason it's not a rain
line or a rain zigzag see you and your
eyes are at the apex of a huge half cone
at the other end is the water that makes
the rainbow this gives a rainbow that
curved shape we all know and love
everything that you see is because that
light is coming back right to where you
are no one else is experiencing exactly
the same rainbow as you if everyone's
rainbow is unique
does your rainbow look like my rainbow
well michael from vsauce has a great
video about that so i'll put a link in
the description and let him answer that
question for you could we ever see a
different rainbow we've evolved to only
see a tiny fraction of one percent of
the entire electromagnetic spectrum what
about all the rest of it from x-rays to
radio waves what if we could see a
rainbow like the mantis shrimp then our
rainbow could stretch across the sky
well spoiler alert maybe not well it's
true that we only see a sliver of the
spectrum you can't make a rainbow out of
anything that doesn't make it into
earth's atmosphere take the sun it
actually emits almost half of its
radiation right around the visible range
which is exactly why we evolved to see
that range
the rest of the sunlight is mostly
infrared and just a tiny bit of uv
if we could see a rainbow made of all of
that
well it would only be about twice the
width of the one we're used to
unfortunately if we could see infrared
we'd be blinded by the infrared
radiation emitted by all the warm things
around us including the earth itself
and turning up the sun wouldn't work
either
most of the electromagnetic spectrum is
actually filtered out before it reaches
earth's surface
what about all those radio waves i mean
they're traveling freely through the
atmosphere picture all those bands way
beyond the red side of our rainbow sadly
having radio antennas for eyes would
also be a blinding experience because
the air is filled with the signals from
our wi-fi mobile phones and
well radio i guess we'll have to be
happy with the rainbow we have because
it's pretty much the best rainbow we can
make the next time you see a rainbow
remember that even though there's no pot
of gold at the end
no one else can see exactly the same
rainbow that you can
and that sounds like treasure to me stay
curious and thanks for watching