Rainbows, Prisms & Lasers: How Light Hides Color

Nova: Buckle up, Explorers.

Cosmo: Brains in!

Nova: Wheels up!

Nova & Cosmo: Brain Bus, let's GO!

Nova: You're on The Brain Bus - I'm Nova, your driver, and today Cosmo and I are taking you somewhere really, really shiny.

Cosmo: I'm Cosmo, robot co-pilot, fact collector, and expert on flavors. I mean, science.

Nova: Here is something that will flip your brain upside down. Every rainbow you have ever seen is actually a full circle - but the ground hides the bottom half, so you only ever see the top arc. From an aeroplane above the clouds, you can sometimes see the whole glowing ring.

Cosmo: A rainbow RING?! Like a hula hoop made of sky?

Nova: Exactly like a hula hoop made of sky. Today, Explorers, The Brain Bus is driving us straight into the world of light and color - rainbows, prisms, and lasers. Hang on tight.

Nova: So - what is a rainbow, really? Cosmo, opening theory?

Cosmo: A rainbow is obviously a giant curved candy arch - every color is a different flavor, and if I could just run fast enough to reach the end, I could take the biggest bite.

Nova: Heartbreaking news: you could run forever and never reach it. A rainbow is not sitting in one place. It is sunlight bouncing around inside thousands of tiny raindrops in the air, aimed right at YOUR eyes. Wherever you walk, it moves with you and stays the same distance away. You will never, ever catch it.

Cosmo: That is deeply unfair.

Nova: Here is the really extraordinary part. Plain white sunshine looks totally empty and colorless - but it is secretly hiding every single color, all squished together at once. Scientists call that white light. Think of it like a vanilla milkshake with all the rainbow colors blended inside - you cannot see them because they are all mixed together.

Cosmo: The raindrop sorts the flavors back out?

Nova: Exactly. A raindrop - or a little glass shape called a prism, say it with me Explorers: prism - bends the light, and because each color bends a tiny different amount, they step out single file into a line. Red first, then orange, yellow, green, blue, violet at the end. That line of colors is your rainbow. The raindrop is nature's prism.

Cosmo: I am filing that in my Data Log - first entry: a raindrop can unmix all the colors hiding in white sunshine. Filed.

Nova: And millions of raindrops do that trick at the exact same moment, painting that giant glowing arc across the sky. Now Cosmo - how many colors are in there?

Cosmo: My Space Guidebook says exactly seven.

Nova: Lots of people say that - but a rainbow is actually a smooth blend where all the colors melt into each other with no hard edges. We named seven to make it easy to talk about, but the real number is way too many to count.

Cosmo: Way too many to count. That is so much better than seven.

Nova: And if you spot a double rainbow - two arcs one above the other - the second arc has its colors flipped backwards. Outside edge violet, inside edge red. Nature being spectacular.

Nova: People have wondered about rainbows forever, and some of the most beautiful ideas come as stories. This one comes to us from the people of Ancient Greece, a civilization that lived thousands of years ago around the Mediterranean Sea. They told stories about a goddess named Iris. They said the rainbow was her path - a glowing bridge she ran along, carrying messages from the gods in the sky down to people on the ground. Because she was so full of color, the Ancient Greeks gave her name to the colored ring inside your eye - the part that makes eyes brown or green or blue. We still call it the iris today.

Cosmo: My eyes have a goddess inside them?

Nova: In a way, yes.

Nova: Just hold that thought for a second, Explorers.

Nova: White light is not plain or empty. All the colors of the rainbow are hiding inside it, always. And a raindrop - something so tiny you can barely feel it on your skin - can spread those colors apart so we can see every single one. That is genuinely one of the most beautiful things I know.

Nova: Light also moves in ways that are hard to imagine. It is the fastest thing in the universe - in one second, it could zoom around the Earth more than seven times. The sunshine warming your face right now actually left the Sun eight minutes ago and has been racing across space ever since to reach you.

Cosmo: Eight minutes ago I was thinking about snacks.

Nova: Scientists have also created something called a laser - everyone say it: laser! A laser is light where every tiny bit is lined up in a perfectly straight beam, all exactly the same color. Lasers are so precise that scientists have aimed one all the way to the Moon and bounced the light right back to Earth. One important rule though - lasers are powerful, so never, ever point one at anyone's eyes. Redirect to wonder instead: picture a beam of light traveling all the way to the Moon and coming home again.

Nova: Here is one more trick light plays. Why does a red apple look red? It soaks up every other color from the light and bounces only the red part to your eyes. That bounced color is what you see. And - here is something wild - bees can see an extra color called ultraviolet that human eyes cannot detect at all. Flowers have secret patterns painted in ultraviolet, just for bees to find them. We are missing a whole layer of the world's color.

Cosmo: Bees are seeing extra things. I am putting bees above me in the rankings.

Nova: Quiz time, Explorers - shout your answers out loud!

Cosmo: I, Cosmo, am your quiz master. This is my moment.

Cosmo: Question one! True or False - a rainbow is really a full circle.

Nova: TRUE! From the ground we only see the top half, but from a high aeroplane you can sometimes spot the whole ring.

Cosmo: Question two! True or False - white light is made of just one plain color.

Nova: FALSE! White light holds every color blended together, and a raindrop or prism pulls them apart.

Cosmo: Question three - multiple choice! What makes a rainbow appear? Is it A - snow, B - raindrops and sunlight, or C - the Moon?

Nova: B - raindrops and sunlight! Each tiny raindrop bends the sunshine and splits it into colors, and millions of drops do it all at once.

Cosmo: Whatever you scored, you thought hard, and that is the whole point. Every Explorer on this bus gets the official Brain Bus thinker badge.

Nova: Four incredible facts - every one of them brand new!

Cosmo: One! The Norse people of Scandinavia told stories about a shimmering rainbow bridge called Bifröst - say it: Bi-frost - that connected the world of people all the way up to the home of the gods, guarded day and night by a watchman named Heimdall.

Nova: Two! Scientists bounced a laser beam off the Moon - and it worked because astronauts left special mirror-like reflectors sitting on the Moon's surface. The Moon has mirrors on it.

Cosmo: Three! A double rainbow's second arc has all its colors flipped backwards - violet on the outside, red on the inside.

Nova: Four! The color you see when you look at anything - a red bus, a blue sky, a green leaf - is the only color that object is bouncing away. It has kept nothing for itself.

Nova: Road Challenge - no looking around, just your brains and your voices!

Nova: We are building a rainbow out of words. For each color in order, everyone shout something that is that color - a food, an animal, anything!

Nova: Ready? RED - shout something red! ORANGE - what is orange? YELLOW - go! GREEN - anything green! BLUE - shout it! PURPLE - last one, make it a good one!

Nova: You just painted a rainbow with your voices.

Nova: Here is your wondering question for the rest of the drive: when the sun goes down and it gets dark and you cannot see any colors anymore - where do all the colors go? Do you even need light to see a color at all?

Nova: Almost time to phase back - but first, the Next-Stop Riddle!

Nova: I can be bigger than a house or smaller than your fingernail. I can move faster than anything on Earth or slower than a snail. Some of my kind weigh more than twenty school buses, and others are so tiny you can barely see them. What am I?

Nova: Hmm. Good thinking out there. We are not revealing the answer today - you will find out next time you hop on The Brain Bus.

Cosmo: I have a guess. It is excellent. It stays in the data banks until then.

Nova: What a journey today, Explorers. White light secretly holding every color. Raindrops spreading them out single file. A rainbow you can never catch because it always moves with your eyes. A goddess named Iris living inside the name of your eye. Lasers bouncing off the Moon. Bees seeing a whole color we cannot.

Nova: The whole rainbow is always there, hiding in every beam of light around you - just waiting for the right doorway.

Nova: Stay curious, stay clever, and keep that brain working!

Nova: Until the next stop, Explorers...

Cosmo: ...keep wondering.