🌈 Do your children keep asking you how a rainbow forms, while you struggle to explain this weather wonder without getting in a muddle? This article breaks down, in simple terms, the optical phenomenon where sunlight plays hide-and-seek with raindrops to paint your sky. You’ll discover the secrets of refraction, the unchanging order of the seven colours, and even a few tricks for making your own multicoloured arch at home with a simple garden hose.
- The ingredients for a beautiful rainbow
- The journey of light inside a water drop
- 7 colours arranged in a very precise order
- Why do we see an arc and not a circle?
- The secret of double rainbows and dark bands
- 3 tricks for making an artificial rainbow
🌈 The ingredients for a beautiful rainbow
After a shower, the sky sometimes treats us to a colourful display, but this phenomenon owes nothing to chance and needs very specific weather conditions.
🌧️ The role of rain and damp air
Rain is the first must-have ingredient. Without water drops, no splitting of light is possible. You need dense enough hanging moisture to create the effect.
A light mist often works better than a thick downpour. The droplets need to be nice and round, and there must be lots of them. They catch the surrounding light to kick off the whole physical process.
The air has to be soaked with water. That’s the very base of this natural mirror.
☀️ Where the sun sits compared with us
There’s a golden rule about where to stand. The sun must always be behind you. Your eyes then face the curtain of rain.
The light hits the drops at a precise angle. That’s what lets the rays split into colours. It’s a matter of pure, simple geometry.
The sunlight must be direct. The rays mustn’t be filtered.
☁️ Why the sky mustn’t be completely grey
A fully clouded sky blocks the direct rays. You need a gap of light to light up the drops. Without it, the phenomenon stays invisible.
The rainbow stands out better against a backdrop of dark clouds. That inky black makes the colours glow. Without that contrast, the result stays dull. The human eye picks up the shades better this way.
Bright sun and pouring rain. That’s the perfect mix.
💧 The journey of light inside a water drop
To understand how these colours are born, you have to follow the path of a single ray of light as it strikes a tiny sphere of water.
💧 Entering the drop, and refraction
The light first travels through the air before it hits the droplet. The moment it enters the water, its surroundings change. Its speed then drops suddenly at that exact instant.
The ray bends sharply as it enters the water. This physical effect is called refraction. Each colour bends differently depending on its own wavelength.
The white light splits apart. The sorting of the colours begins here.
🔄 The internal reflection on the back wall
The ray carries on to the bottom of the sphere. It then hits the inner wall on the far side. It doesn’t come straight out into the open air on the other side.
The back wall acts like a real mirror. The light bounces back towards the front of the drop. This technical step is called total internal reflection, a bounce that the whole effect depends on.
The water drop behaves like a tiny liquid mirror that sends the light back to the observer after splitting it apart.
✨ The exit and the final spreading of the rays
As it leaves the water for the air, the ray bends a second time. This new bend widens the gap between the shades. Red and violet move even further apart.
The rays come out in a fan towards your eyes, creating those coloured bands. You then see the full spectrum. Each drop gives one precise colour, but all of them together create the overall picture of the rainbow.
The white light has become multicoloured. The journey is over.
🎨 7 colours arranged in a very precise order
Once the light is split, it doesn’t mix at random but follows an unchanging order of colours.
🔆 The natural splitting of white light
Each little raindrop acts like a tiny prism. Isaac Newton proved this a long time ago. White light actually hides every colour inside it.
Here’s the order you always see in the primary rainbow:
- Red (on the outside)
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet (on the inside)
The change is smooth. The shades blend into one another. It’s a continuous gradient.
📐 From red to violet: a question of angle
It all comes down to how much the light bends. Red is the colour that bends the least. Violet, on the other hand, bends the most.
Physics sets strict rules. The rays come out at angles of 42.4° for red and 40.5° for blue.
These fixed angles decide the position. Red is always at the top of the arch. Blue stays at the bottom.
👁️ The difference between the eye and pure physics
Let’s talk a little about how we humans see. The spectrum is really a continuous ribbon. Yet our brain prefers to cut it into separate bands.
The retina has cones that are sensitive to certain wavelengths. We then read these electrical signals as colours. It’s something our nervous system builds. Physics itself only knows frequencies. So how does a rainbow form, in simple terms? Above all, it’s a personal experience.
It’s a lovely illusion. Nature gives us waves. We see shades in them.
⭕ Why do we see an arc and not a circle?
If the colours are clear, their shape often raises a question: why does this perfect half-circle seem to rest on the horizon?
🌅 A full circle hidden by the earth’s horizon
In reality, the rainbow is a complete circle. Physics demands perfect radial symmetry. It isn’t just a line that happens to be curved.
The ground cuts off the lower part of the circle. We only see the top half. The horizon acts like a visual mask. It’s a physical limit of our point of view. The lower the sun, the bigger the arc.
It all rests on the cone of light and the antisolar point. It’s pure maths.
🚶 Why you can’t reach the foot of the arch
The rainbow doesn’t exist in a fixed spot. It’s a purely optical illusion made of light. There’s no solid object to touch over there.
If you move forward, the rainbow moves back with you. It depends on your exact position. You are the centre of your own rainbow. So everyone sees their own version.
Forget the pot of gold. Nobody will ever touch the foot of the arch. It’s a fleeting mirage.
✈️ The perfect geometry seen from a plane
From a plane, the ground is no longer in the way. You can then see the whole circle. It’s a treat saved for those who gain some height.
The circle often surrounds the shadow of the aircraft. It’s a rare and beautiful sight. The geometry then shows itself in full. There’s no more cut-off from the ground. The cone of light is finally complete.
Gaining height changes everything. The shape becomes perfect. It’s a question of perspective.
🔍 The secret of double rainbows and dark bands
Sometimes nature doubles up and shows a second, fainter rainbow just above the first.
🔁 The double reflection behind the secondary rainbow
The light can reflect twice. It hits two inner walls before coming out. It’s this extra bounce that creates the magic.
Each bounce soaks up a little energy. So the second rainbow is paler. It sits about ten degrees higher. It’s a rarer thing to spot.
You can better picture the light’s path with this idea of the secondary rainbow. It’s both mathematical and poetic.
🔃 Why the colours are reversed at the top
This extra bounce reverses the order of the shades. It’s a direct result of the geometry. The light simply comes out by a different path.
This time, violet ends up on the outside. Red shifts towards the inside of the arc. It’s the perfect mirror of the first rainbow.
In the secondary rainbow, the complex path of the light ends up completely reversing the usual order of the colours.
🌑 The mystery of Alexander’s dark band
Between the two rainbows, the sky looks darker. It’s called Alexander’s band. It’s a contrast that often surprises people out walking.
In this space, no ray is sent back. The light is bent either higher or lower. It’s an optical gap between the two phenomena. This detail is fascinating for observers.
The black is deeper there. It’s a physical signature. That’s how a rainbow forms: a simple explanation of a gap in the light.
🛠️ 3 tricks for making an artificial rainbow
You don’t need to wait for a storm to enjoy these colours; you can recreate this wonder at home with a few simple objects.
💦 Using a garden hose in the garden
For this method, stand with your back to the sun on a sunny day. Just set your hose to a very fine spray. The idea is to create a light, steady mist.
Spray the water in front of you in an arc. Look for the angle where the colours suddenly burst out. It’s often quite low, near the ground. Play with how fine the drops are. The smaller they are, the softer the colours.
There you have your own personal rainbow. It’s instant and very rewarding.
🔦 The glass of water and torch experiment
Here’s a very easy indoor tutorial. Fill a big glass with clean water. Then put it on a table, right next to a sheet of white paper.
Shine a powerful torch at the glass. The colours will be cast onto the white paper. Gently adjust the distance for a sharper result.
| Method | Equipment | Difficulty | What to expect |
|---|---|---|---|
| Garden hose | Jet of water | Very easy | Big outdoor arc |
| Glass of water | Torch | Easy | Spectrum on paper |
| Crystal prism | Direct sun | Medium | Very pure colours |
🧒 Explaining the phenomenon to children simply
For little ones, use playful comparisons. Talk about a slide for the light. The rays slip over the drops and split apart for fun to show off their colours.
Explain that the rainbow isn’t a solid bridge. You can’t walk on it. Talk too about moonbows, which are rarer. They form at night with moonlight. It’s magical, but much paler.
Science explains the beauty. It never takes it away.
To enjoy this display, keep the sun at your back, facing the rain. The light then reflects and splits inside each droplet. Quick, grab your garden hose to make your own rainbow and amaze your little explorers today!
❓ FAQ
🌦️ What are the ideal conditions for seeing a rainbow?
To enjoy this lovely display, you need to bring together two simple ingredients: rain (or mist) and bright sun. The secret is where you stand. The sun must always be behind you, while you look towards the curtain of water in front of you.
The perfect moment? It’s often when the sky is very dark on one side and the sun breaks through on the other. This contrast of light makes the colours stand out incredibly well, to the delight of children and grown-ups alike.
🎨 Why are the colours of a rainbow always in the same order?
It’s a matter of very precise physics! The white light of the sun splits as it goes through each water drop. Since each colour bends at a different angle, red always ends up on the outside of the arc and violet on the inside.
In the primary rainbow, you’ll always see the same sequence: red, orange, yellow, green, blue, indigo and violet. It’s an unchanging order every single time.
⭕ Is it true that a rainbow is actually a complete circle?
Yes, it’s completely true! The arc shape we see from the ground is an illusion caused by the horizon. The earth simply cuts off the lower part of this big circle of light.
If you’re lucky enough to fly during a sunny shower, look carefully out of the window. With no ground to block the view, you can sometimes spot a perfect coloured circle surrounding the shadow of the aircraft.
🌈 Why do we sometimes see a second rainbow above the first?
This is what we call a secondary rainbow. It forms when the light bounces twice inside the water drops instead of just once. This second journey makes the rainbow a little paler and higher in the sky.
A fun little detail to spot with your children: in this second rainbow, the order of the colours is completely reversed! Red ends up on the inside and violet on the outside. It’s the mirror image of the first.
👣 Can you really reach the foot of a rainbow?
Sadly for the pot-of-gold legend, it’s impossible. A rainbow isn’t a physical object sitting in one precise spot, but an optical illusion that depends on your own gaze.
Since the rainbow moves along with you, it will always stay the same distance away. You are, in a way, the centre of your very own personal rainbow; it follows you everywhere you go!
⚫ What is the darker area between the two rainbows?
If you look carefully at a double rainbow, you’ll notice that the space between the two coloured bands looks darker than the rest of the sky. It’s called Alexander’s dark band.
This happens because the water drops send almost no light back to your eyes in that particular area. It’s a little gap of light that makes the display even more striking.
