Sometimes the sky displays a breathtaking spectacle where a rainbow appears to stretch across the clouds like a streak of fire. This rare phenomenon is often called a “fire rainbow.”
This rare phenomenon, often called a fire rainbow, is actually a scientific event known as a circumhorizontal arc.
Nature produces many mysterious phenomena, from the blue fire volcano at night to the strange river flowing beneath the ocean.
Despite its dramatic appearance, this glowing arc is not actually fire, and it isn’t a true rainbow either. It is a fascinating atmospheric optical effect known as a circumhorizontal arc.
What Is a “Fire Rainbow”?
A fire rainbow, scientifically called a circumhorizontal arc, is an atmospheric phenomenon created when sunlight passes through ice crystals in high-altitude clouds.
These arcs appear as bright bands of color that run parallel to the horizon and often resemble flames spreading across the sky.
Although the name suggests otherwise, they are not caused by fire or rain. The term simply comes from their fiery appearance and vivid colors.
How This Rare Sky Phenomenon Forms
For a circumhorizontal arc to appear, several specific conditions must occur at the same time.
First, the sun must be high in the sky — typically more than about 58° above the horizon.
Second, the sky must contain thin cirrus clouds, which are high-altitude clouds made of tiny hexagonal ice crystals.
When sunlight enters these flat ice crystals, it bends (refracts) and separates into different colors, producing a bright spectrum similar to a rainbow.
Because the ice crystals act like tiny prisms, the light spreads into vivid colors that can stretch across the sky.
Why It Looks Like Flames in the Sky
The colors produced by a circumhorizontal arc are often extremely vivid. In many cases the arc appears fragmented within clouds, giving it a shape that resembles flames or burning streaks in the sky.
This effect creates the illusion that a rainbow is on fire — which is why the term “fire rainbow” became popular online.
However, the phenomenon is actually part of a family of atmospheric halo effects caused by light interacting with ice crystals in the atmosphere.
Why Fire Rainbows Are Rare
Although they are spectacular, fire rainbows are relatively uncommon because several conditions must align perfectly:
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The sun must be very high in the sky
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Thin cirrus clouds must be present
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Ice crystals must be aligned horizontally
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The viewing angle must be correct
Because of these strict conditions, many people may go years without seeing one.
A Beautiful Reminder of Nature’s Physics
While a fire rainbow may look magical or even supernatural, it is actually a stunning demonstration of how sunlight interacts with Earth’s atmosphere.
From ice crystals drifting miles above the ground to the precise angle of sunlight, this phenomenon reveals how complex and beautiful atmospheric physics can be.
If you ever see a rainbow that looks like it’s burning across the sky, you’re witnessing one of the most spectacular optical illusions nature can create.
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