The Science of Rainbows: Why They Appear, How They Form, and What They Really Are

Imagine this: you're standing there after the rain looking at the sky, and there's this thing hanging there – a rainbow. Beautiful, bright, as if someone smeared a giant set of watercolors across the sky. And you think: «Wow, what beauty!»» But I think: «Wow, what a perfect optical deception!»» Because a rainbow isn't what you see. Or rather, it is exactly what you see, but not at all where you think it is. And now I'm going to explain why your brain and millions of water droplets have staged this performance for you.

Light Is Not White It's a Lie

Light is not white, it's a lie 🌈

Let's start with the basics: white light is a fake. Seriously. When the sun shines on your face, you see white light, but in reality, it's a mixture of all the colors of the rainbow packed into a single beam. It's like you bought an «Everything at Once»» cocktail and then act surprised that there are seven flavors simultaneously.

Isaac Newton discovered this in 1666 when he locked himself in a dark room with a prism and decided to play around with light. He aimed a sunbeam at a glass prism, and – bam! – the white light turned into a rainbow on the wall. Newton realized: light consists of different colors that just travel together, like a group of tourists on a bus. As long as everything is going in a straight line, they stick together. But as soon as the bus takes a sharp turn (meaning the light hits a different medium – glass, water), every color starts behaving in its own way.

Why does this happen? Because different colors are waves of different lengths. Red light is long, lazy waves; violet is short and nervous ones. When they enter water or glass, their speed changes, and not equally. Violet brakes harder, red brakes less. And because of this, they scatter in different directions, like drunk friends after a party, each going their own way.

A Water Drop Is a Hooligan Lens

A water drop isn't just a drop, it's a hooligan lens

Now picture a raindrop. Small, round, hanging in the air. Looks innocent, right? Yeah, right. That drop is a veritable optical laboratory. When a sunbeam hits it, the circus begins.

Here's what happens step-by-step:

1. The beam enters the drop. Light flies through the air at a speed of about 300,000 kilometers per second (fast, but not infinitely fast). When it hits water, the speed drops to about 225,000 kilometers per second. Because of this braking, the beam changes direction – this is called refraction. And immediately, the white light starts breaking down into colors because each color brakes slightly differently.
2. The beam travels inside the drop. Now it's no longer white, but a multicolored fan of rays flying through the drop to its back wall.
3. The beam reflects off the back wall of the drop. Imagine the drop is a mirror ball at a disco. The beam hits the back surface and bounces back. Moreover, the reflection happens at a very precise angle – about 42 degrees relative to the direction the sunlight came from.
4. The beam exits the drop. On the way out, it refracts again, and the colors separate even further. Now it's not just a fan, but a full-blown spectrum – from red to violet.

This whole story takes a fraction of a second, but the result is impressive: a rainbow beam shoots out of the drop and flies straight into your eye. And there are millions of such drops around. Each works like a tiny projector, showing you its own little piece of the spectrum.

Why Is a Rainbow an Arc and Not a Straight Line?

Why is a rainbow an arc and not a straight line?

Good question. Why not a strip, not a square, but specifically an arc? The answer is simple: geometry and your position.

Remember that 42-degree angle? That's the key to everything. Every drop sending red light to you is located exactly at a 42-degree angle from the imaginary line connecting the sun, your head, and the opposite point in the sky (this is called the antisolar point). Violet light comes at a slightly smaller angle – about 40 degrees.

Now imagine: you're standing on the ground, the sun is behind your back, and there are millions of drops in front of you. Those drops located exactly at a 42-degree angle from the antisolar point form a circle around that point. You only see part of this circle – an arc – because the bottom part is hidden by the horizon. But if you were standing on a mountain or flying in a plane, you'd see a full circle. A circular rainbow. Mind-blowing, right?

That's why a rainbow always appears on the opposite side of the sky from the sun. If the sun is behind you, the rainbow is in front. If the sun is to your right, there will be no rainbow because the geometry doesn't add up.

Seven Colors Is a Myth Newton Invented

Seven colors is a myth Newton invented

Red, orange, yellow, green, blue, indigo, violet. We all know this. But here's the secret: there aren't «seven colors»» in a rainbow. There is an infinite number of shades flowing smoothly into one another. The spectrum is continuous.

Newton chose exactly seven colors because he loved the mysticism of numbers. Seven is the number of days in the week, notes in a scale, celestial bodies known in his time. He even shoehorned in «indigo»» (which we now call light blue or dark blue, because most people don't see the difference) to get that sacred seven.

Actually, a rainbow is a gradient. A smooth transition from long waves (red) to short ones (violet). Between red and orange, there are a million shades. Between green and blue, too. But the human brain loves to simplify, so we break the spectrum into convenient categories and say: «This is red, and that is yellow»». Convenient, but inaccurate.

Double Rainbow When the Drop Decides to Show Off

Double rainbow – when the drop decides to show off

Sometimes you see not one rainbow, but two. One bright, the other paler and higher up. And the colors in the top one are flipped: red at the bottom, violet at the top. What the hell is that?

This happens when light reflects inside the drop not once, but twice. Imagine: the beam enters the drop, reflects off the back wall, but instead of exiting immediately, it bounces off the front wall one more time, and only then exits. This is double reflection.

Because of the second reflection, the exit angle of the beam changes – it becomes larger, about 51 degrees. That's why the second rainbow appears higher than the first. And the colors flip because the path of light inside the drop changed. Red, which is usually on top, is now at the bottom. Violet, which is at the bottom, is now on top.

The second rainbow is always paler because with each reflection, part of the light is lost. Two reflections equal more losses, less brightness. Simple physics.

And there is also a zone between the two rainbows that seems darker than the rest of the sky. It is called «Alexander's band»», after the ancient Greek philosopher Alexander of Aphrodisias, who first described it. It's darker because almost no reflected light gets there – all the energy goes into the bright arcs above and below.

Why Can't a Rainbow Be Photographed the Way You See It?

Why can't a rainbow be photographed the way you see it?

Have you ever tried to take a picture of a rainbow? It looks cool in real life, but in the photo, it's always somehow... paler. Dimmer. Less impressive. Why?

Because a camera and your eye work differently. Your eye is an adaptive system. It automatically adjusts sensitivity, contrast, and color rendering. When you look at a rainbow, your brain boosts the brightness of the colors, making them juicier. It's not a trick – it's just how perception works.

The camera records light «as is»». It doesn't know that a rainbow is something special. To it, it's just another patch of sky with slightly increased intensity of certain wavelengths. Plus, most cameras don't cover the full dynamic range of the scene: if the sky is bright, the rainbow becomes pale; if you expose for the rainbow, the sky gets blown out.

That's why your friends on Instagram photoshop rainbows to an indecent degree. They aren't lying – they're just trying to convey what they saw with their eyes.

Rainbows at Night Moonbows and Other Oddities

Rainbows at night, moonbows, and other oddities

Can you see a rainbow at night? Yes. If the moon is bright enough (usually full or close to full), and if there is rain or water mist (for example, near a waterfall), you can see a lunar rainbow, or «moonbow»».

It works exactly like a regular rainbow, only the light source isn't the sun, but the moon. True, moonlight is hundreds of thousands of times weaker than sunlight, so a moonbow almost always looks pale, almost white. Your eyes switch to rods in the dark – light-sensitive cells that don't distinguish colors. So you only see a faint white arc. But if you take a picture with a long exposure, the camera will capture the colors. They are there, the eye just doesn't see them.

And then there are fog rainbows – «fogbows»». They appear when light passes through fog, where the droplets are so tiny that they barely separate light into colors. The result is a white or slightly colored arc. Ghostly, as if someone drew it with chalk on the gray sky.

A Rainbow Isn't an Object It's an Illusion

A rainbow isn't an object, it's an illusion

Here's the weirdest part: a rainbow doesn't exist in space. You can't touch it, you can't get closer to it. It's not an object, but a phenomenon – a picture created by the interaction of light, water droplets, and your position.

If you take a step to the left, the rainbow moves. If your friend is standing nearby, he will see his own rainbow created by other droplets. Two identical rainbows cannot exist simultaneously because a different set of drops works for each observer.

It's like a reflection in a mirror: you see it, but if you try to touch it, there's nothing there. A rainbow is your personal optical show, arranged by the universe specifically for you. Romantic, right? Although physicists would say: «It's just geometry and refraction»». But where's the romance in that?

Artificial Rainbows and How to Make Them at Home

Artificial rainbows and how to make them at home

Want to make a rainbow right now? Easy. You need three things: a light source (sun or bright lamp), water (spray bottle, hose, even a glass), and the right angle.

Stand with your back to the sun. Take a hose with a spray nozzle and start spraying water in front of you. That's it, the rainbow will appear. It will be small, but real. These are the same drops, the same refraction, the same 42 degrees. Physics doesn't care about scale.

And if you have a prism (or even an old CD) at home, aim a sunbeam at it. The prism will decompose the light into a spectrum, and you will see a rainbow on the wall. It's not quite the same as water drops, but the principle is the same: different colors refract differently.

By the way, rainbows also happen in fountain sprays, in dewdrops on a spiderweb, and even in diamonds (there they are called «fire»»). Wherever light passes through a transparent medium with a change in speed, a chance arises to see this colorful spectacle.

What Does a Rainbow Tell Us About the World?

What does a rainbow tell us about the world?

A rainbow isn't just a beautiful natural phenomenon. It's a physics lesson that the sky teaches us for free. It shows that light is waves, that color is wavelength, that matter (water) can change the behavior of light. It demonstrates refraction, reflection, dispersion – all the basic principles of optics – right over your head.

And it also reminds us that reality is more complex than it seems. What you see (an arc in the sky) isn't what is actually there (millions of drops, each reflecting light at a specific angle). Your brain assembles an ordered picture – a rainbow – out of this chaos. And this picture is beautiful precisely because it isn't real. It is an interpretation created by your perception.

So next time you see a rainbow, don't just take a picture for Instagram. Think about the fact that you aren't seeing an object, but a process. Not a painting, but the interaction of light, water, and your unique position in space. It's not magic – it's physics. But damn beautiful physics.

The Final Touch The Rainbow as a Metaphor

The final touch: the rainbow as a metaphor

People love to use the rainbow as a symbol. Hope, peace, diversity – all this is the rainbow. But from a physics point of view, a rainbow is simply light that couldn't go straight. It hit an obstacle (a water drop), changed direction, fell apart, reflected, refracted twice – and only after all these torments did it create something beautiful.

Maybe this is the real metaphor: beauty isn't born from a straight path, but from complex interactions, from obstacles, from the fact that light didn't give up and found a way to show itself in the full spectrum. Although, maybe I just drank too much espresso.

Alright, I'm done. Go find a rainbow. Just remember: it isn't waiting for you at the end – it only exists because you are standing exactly where you are standing. 🌈