How Rainbow is Formed? Discover the Different Types of Stunning Rainbows!

Photo by Frans van Heerden

Rainbows are one of the most magical things nature gives us. They show up after a fresh rain, painting the sky with colors that make everything feel a little more special. But have you ever stopped to think about how rainbow is formed? It’s not just a random splash of colors; it’s pure science at work. Rainbow formation happens when light bends, bounces, and breaks apart in raindrops, creating the beautiful arc we see. A rainbow isn’t just one thing, though. There are different types, and each has its own way of forming.

Some rainbows are bright and easy to see, while others are rare and only show up in special conditions. There are even double and upside-down rainbows! If you’ve ever been curious about what makes them happen, let’s break it down in the simplest way possible. This is the complete guide to understanding rainbows—what they are, how they form, and the different types you might see.

The Science Behind a Rainbow: How Light Creates Colors

KES47, Public domain, via Wikimedia Commons

When sunlight passes through raindrops, something amazing happens. The light bends (refraction), bounces inside the droplet (reflection), and then spreads out into different colors (dispersion). This entire process is what makes a rainbow.

It all starts with refraction. When light enters a raindrop, it slows down and bends because water is denser than air. This bending causes the light to spread out into different colors. Each color bends at a slightly different angle, which is why we see them separately.

Next comes reflection. The bent light hits the inside surface of the raindrop and reflects back, changing direction. This bouncing is what allows us to see the rainbow from the ground. If the light didn’t reflect, it would just pass through, and no rainbow would form.

Finally, dispersion happens. As the light exits the raindrop, it bends again. Because each color bends at a different angle, they spread out into the classic rainbow sequence: red, orange, yellow, green, blue, indigo, and violet (ROYGBIV).

Why Do Rainbows Always Form in an Arc?

Rainbows aren’t just random streaks of color in the sky. They always appear in a curved shape because of the way light interacts with raindrops. The key to this lies in angles and our perspective.

When sunlight enters a raindrop, it refracts, reflects, and then disperses. But for us to see a rainbow, the light must leave the droplet at a precise angle—around 42 degrees for red light and slightly less for violet light. Since raindrops are spherical, they scatter light in all directions. However, only the light coming at the right angle reaches our eyes, creating a curved shape.

The rainbow isn’t actually an arc; it’s a full circle! We usually see only the top half because the ground blocks the rest. If you were high up, like in an airplane or on a mountain, you might see a full circular rainbow. The next time you spot a rainbow, remember—it’s not just a colorful band, but a perfect ring hiding beneath the horizon.

Why Some Rainbows Are Brighter Than Others?

Image by @visitfairfieldca

Not all rainbows look the same. Some are super bright and vivid, while others are faint and hard to spot. The reason for this comes down to three main things: the size of the raindrops, the intensity of the sunlight, and the cleanliness of the air.

Bigger raindrops create brighter rainbows because they allow more light to reflect inside. Small raindrops, like mist or drizzle, make rainbows that are dim and blurry. This is why rainbows during a light drizzle often look weaker compared to those after a heavy rain.

The angle of the sun also matters. If the sun is too high, the rainbow disappears. The best rainbows happen when the sun is lower in the sky—early morning or late afternoon.

Lastly, air quality affects how sharp a rainbow looks. If there’s a lot of dust, pollution, or fog, the light gets scattered, making the rainbow appear faded. But on a clear day, with strong sunlight and large raindrops, you get the most vibrant, picture-perfect rainbow.

What Causes a Double Rainbow?

Image by @sof1bee

Seeing a double rainbow feels like a rare and magical moment. But what actually causes it? It all comes down to how many times light bounces inside a raindrop.

In a normal rainbow, light enters a raindrop, bends, reflects once inside, and exits—creating the standard arc of colors. But sometimes, light bounces twice inside the droplet before exiting. This second reflection creates a second rainbow above the first one.

A double rainbow has a few key differences from a regular one:

The second rainbow is fainter. Since the light reflects twice, some of it is lost, making the second arc dimmer than the first.
The colors are reversed. In the first rainbow, red is on top and violet is at the bottom. In the second one, it’s the opposite—violet is on top and red is at the bottom.
It’s wider apart. Because of the second reflection, the angle of light changes, making the second rainbow appear larger and farther from the first.

Double rainbows happen when there are large raindrops and strong sunlight at just the right angles. The next time you see one, remember—it’s not just luck; it’s science playing tricks with light!

What Is a Supernumerary Rainbow?

Mika-Pekka Markkanen, CC BY-SA 4.0, via Wikimedia Commons

Ever seen a rainbow with extra bands of colors inside it? That’s called a supernumerary rainbow, and it’s one of the rarest types. Instead of just the usual seven colors, these rainbows have additional, thinner bands of pink, green, or purple right under the main arc.

Unlike regular rainbows, which are caused by simple refraction and reflection, supernumerary rainbows happen because of wave interference. When light waves pass through small raindrops (smaller than 1mm), they overlap and interfere with each other. Some waves strengthen each other (constructive interference), while others cancel out (destructive interference). This creates the extra bands of colors.

Supernumerary rainbows have a few unique traits:

They only appear under the main rainbow (never above).
The extra bands are pastel-like and don’t follow the typical ROYGBIV order.
They happen more often when the air is very clean, like after a fresh rain in the countryside.

If you ever spot one, you’re witnessing a rare mix of physics and nature!

What Is a Moonbow (Lunar Rainbow)?

Image by @clairetakacs

Rainbows don’t just happen during the day. When the moon is bright enough, it can create a moonbow, also known as a lunar rainbow. It’s the same process as a regular rainbow, but instead of sunlight, it’s caused by moonlight reflecting off raindrops.

Since moonlight is much dimmer than sunlight, moonbows are usually faint and colorless. The colors are still there, but our eyes struggle to see them in low light. Most of the time, a moonbow looks like a pale white arc in the night sky. However, if you take a long-exposure photo, the full spectrum of colors becomes visible.

Moonbows are pretty rare because they need just the right conditions:

A bright, almost full moon
Rain or mist in the opposite direction of the moon
A dark sky with little to no light pollution
The moon has to be low in the sky (just like with a regular rainbow)

You’re most likely to see a moonbow near waterfalls at night, where mist is always present. Some famous spots include Victoria Falls (Africa) and Cumberland Falls (USA).

What Is a Fogbow? (White Rainbow)

Image by @melvinnicholsonphotography

A fogbow is like a ghostly version of a rainbow. Instead of bright, vivid colors, it appears as a white or pale arc in the mist. Some people even call it a “white rainbow.”

Fogbows happen when light passes through tiny water droplets in fog or mist. Since these droplets are much smaller than raindrops (often less than 0.05mm), they don’t break light into strong colors like a regular rainbow. Instead, they create a faint, almost colorless arc. If there’s any color, it’s usually a soft reddish tint on the outer edge and bluish on the inner edge.

You’re most likely to see a fogbow:

Near waterfalls, where mist is always in the air
Over the ocean, especially in the morning (these are called sea bows)
On foggy mountain roads when sunlight starts breaking through

Fogbows feel more mysterious than rainbows. They don’t have the same bright, happy look, but they’re just as breathtaking when you spot one in the right conditions.

What Is a Circumhorizontal Arc? (Fire Rainbow)

Image by Scott Hefti

A circumhorizontal arc, often called a fire rainbow, isn’t actually a rainbow at all. It’s a rare optical phenomenon that looks like a rainbow streaking across the sky, usually appearing in wispy cirrus clouds.

Fire rainbows happen when sunlight passes through ice crystals in high-altitude clouds. The crystals act like tiny prisms, bending the light and creating a spectrum of colors. Unlike regular rainbows, which form in raindrops, circumhorizontal arcs only appear when the sun is very high in the sky (above 58°).

Here’s what makes them special:

They are flat and horizontal, not curved like a typical rainbow.
The colors are vivid and bright, often more intense than a regular rainbow.
They only form in specific weather conditions, so they’re rare in many parts of the world.

Fire rainbows are most common in summer and are easiest to see in places with wide-open skies. If you ever spot one, you’re witnessing one of nature’s most stunning light shows.

What Is a Glory? (Circular Rainbow Around a Shadow)

Image by @gardensbythebay

A glory looks like a small, circular rainbow that surrounds a shadow—often a person’s shadow on clouds, mist, or fog. It’s sometimes called the “Buddha’s Light” or “Pilot’s Halo” because airplane passengers often see them around the plane’s shadow.

Glories form when sunlight is scattered backward by tiny water droplets in mist or clouds. Unlike normal rainbows, which form from large raindrops, glories are created by much smaller droplets. This makes them look like glowing halos instead of full arcs.

Key features of a glory:

It has concentric rings of color (red on the outside, blue on the inside).
It’s always centered around the observer’s shadow.
The smaller the water droplets, the larger the glory appears.

You’re most likely to see a glory when hiking on a foggy mountain, flying in an airplane, or near misty waterfalls. If you ever spot one, it’s a surreal experience—almost like seeing a rainbow designed just for you.

What Is a Reflection Rainbow?

Image by @earthskyscience

A reflection rainbow happens when a rainbow forms near a large, calm body of water, like a lake or the ocean. It looks like a normal rainbow but with an extra, fainter arc above or below it.

Here’s how it works:

A regular rainbow forms in the sky as sunlight bends through raindrops.

At the same time, some of that sunlight reflects off the water’s surface and enters raindrops at a slightly different angle.

This reflection creates a second, mirrored rainbow that appears either above or below the original one.

Reflection rainbows have a few unique traits:

They are brighter and clearer when the water is smooth and still.
Unlike double rainbows, their colors don’t flip—they remain in the same order.
They usually appear over large, open water bodies where sunlight can reflect properly.

If you ever see a rainbow over a lake or ocean, look closely—you might just spot its ghostly twin hovering nearby.

What Is a Twinned Rainbow?

Elf, CC BY-SA 4.0, via Wikimedia Commons

A twinned rainbow looks like two rainbows that split from the same base. Unlike a double rainbow, where the second arc is separate and has reversed colors, a twinned rainbow shares the same colors and appears to branch out from a single point.

This rare phenomenon happens when raindrops of different sizes are present in the same area. Normally, all raindrops are about the same size, creating a single rainbow. But if there’s a mix of small and large droplets, light bends differently inside them, forming two rainbows that start together but then diverge.

Twinned rainbows have a few key traits:

They come from the same base, unlike double rainbows.
The colors are in the same order (no reversal like in a double rainbow).
They are extremely rare, needing just the right mix of raindrop sizes.

If you ever spot one, consider yourself lucky! It’s a unique trick of light and water that doesn’t happen often.

What Is an Upside-Down Rainbow? (Circumzenithal Arc)

Image by @beingdarcy

An upside-down rainbow, also known as a circumzenithal arc, looks like a rainbow flipped on its head. Instead of a typical arc, this one curves upward, almost like a giant, colorful smile in the sky.

Unlike regular rainbows, which form in raindrops, circumzenithal arcs happen when sunlight passes through ice crystals in high-altitude cirrus clouds. The ice crystals act like prisms, bending the light at precise angles. This only happens when:

The sun is low in the sky, usually below 32° elevation.

The sky is clear, except for thin cirrus clouds.

The ice crystals are perfectly aligned to refract light upward.

Circumzenithal arcs have some cool features:

They are more vivid than regular rainbows.
They only last a few minutes before fading.
They never touch the ground—they appear high in the sky, detached from the horizon.

These rare “sky smiles” are easy to miss because they form above us, but if you ever see one, it’s a sight you won’t forget.

Final Thoughts

Rainbows are more than just beautiful sights after a storm. They are a mix of science and wonder, created by the perfect balance of light, water, and angles. From the common primary rainbow to the rare moonbow, fogbow, and fire rainbow, each type has its own unique story.

Understanding how rainbow is formed makes it even more special when you see one. Whether it’s a double rainbow after heavy rain, a glory surrounding your shadow, or an upside-down circumzenithal arc, these optical wonders remind us that nature is full of surprises.

So next time you spot a rainbow, take a moment to appreciate it. Look closely—there might be a second one, a supernumerary arc, or even a rare twinned rainbow hiding in plain sight. Nature is always putting on a show, and rainbows are one of its best performances.

Have you ever seen a rare type of rainbow? Let’s talk about it in the comments!