Sky Oddities • Atmospheric Optics • Rainbow & Arc Phenomena
Fire rainbows are bright, rainbow-colored atmospheric arcs that appear in high clouds. Despite the dramatic name, they are not fire and they are not true rainbows. They are usually circumhorizontal arcs created when sunlight passes through plate-shaped ice crystals in cirrus clouds.
TL;DR: What Is a Fire Rainbow?
A fire rainbow is the popular name for a circumhorizontal arc, an atmospheric optical phenomenon caused by sunlight refracting through flat ice crystals in high clouds. It appears as a bright, horizontal, rainbow-colored band, usually when the Sun is high in the sky.
The “Rainbow Cloud” That Looks Like the Sky Caught Fire
Fire rainbows can look unreal: glowing strips of red, orange, yellow, green, blue and violet stretched across wispy clouds. They often appear like burning clouds, rainbow flames or a tear in the sky’s graphics card.
The effect is natural, but the name is misleading. A fire rainbow is not caused by flames, heat or rain. It is an ice crystal optical phenomenon created by sunlight passing through high-altitude cirrus clouds.
What Causes a Fire Rainbow?
Fire rainbows form when sunlight enters horizontally oriented, plate-shaped ice crystals and exits through a different crystal face. This bends and separates the sunlight into colors, producing a bright arc below the Sun.
- Sunlight provides the white light.
- Plate-shaped ice crystals act like tiny prisms.
- High cirrus clouds provide the ice-crystal layer.
- Refraction bends the light.
- Dispersion separates the light into colors.
Unlike ordinary rainbows, which require water droplets and a low Sun behind the observer, circumhorizontal arcs require ice crystals and a high Sun.
Best Conditions for Seeing Fire Rainbows
Fire rainbows need a very specific combination of sky conditions.
- The Sun must be high in the sky.
- Thin cirrus or cirrostratus clouds must contain ice crystals.
- The ice crystals must be plate-shaped and horizontally aligned.
- The sky must be bright enough for the colors to stand out.
- The observer must be in the right position relative to the Sun and cloud layer.
This is why fire rainbows are more common in some seasons and latitudes than others.
Fire Rainbow vs Regular Rainbow vs Sundog
| Phenomenon | Real Name | Main Cause | Appearance |
|---|---|---|---|
| Fire rainbow | Circumhorizontal arc | Sunlight through plate-shaped ice crystals | Bright horizontal rainbow-colored band |
| Regular rainbow | Primary rainbow | Sunlight through water droplets | Curved arc opposite the Sun |
| Double rainbow | Secondary rainbow | Two internal reflections in raindrops | Second faint arc with reversed colors |
| Sundog | Parhelion | Sunlight through ice crystals beside the Sun | Bright colored patch left or right of the Sun |
| Circumzenithal arc | Circumzenithal arc | Sunlight through plate-shaped ice crystals | Upside-down rainbow high overhead |
Why Are They Called Fire Rainbows?
The phrase “fire rainbow” is a popular media nickname. It became common because these arcs can make clouds look like they are glowing or burning with color.
Scientifically, the better term is circumhorizontal arc. That name describes the geometry of the phenomenon more accurately: a colorful arc roughly parallel to the horizon, produced by light passing through ice crystals.
How to Recognize a Fire Rainbow
- It appears as a horizontal rainbow-colored band, not a full curved bow after rain.
- It often forms in thin, wispy high clouds.
- It is usually seen when the Sun is high.
- It may look like a rainbow cloud, colorful flame or glowing sky streak.
- It is caused by ice crystals, not raindrops.
Why Fire Rainbows Go Viral
Fire rainbows are perfect viral sky phenomena because they look artificial, colorful and slightly impossible. A bright circumhorizontal arc can resemble burning clouds, chemical spraying, portal light, auroras, UFO effects or an atmospheric glitch.
But the giveaway is usually structure: a bright horizontal band in high clouds, with rainbow colors arranged by light refraction. Strange? Absolutely. Supernatural? The ice crystals would like a word.
Fire Rainbows FAQ
What is a fire rainbow?
A fire rainbow is the popular name for a circumhorizontal arc, a rainbow-colored atmospheric optical phenomenon caused by sunlight passing through plate-shaped ice crystals.
Are fire rainbows real rainbows?
No. Fire rainbows are not true rainbows because they are caused by ice crystals, not water droplets.
What causes a circumhorizontal arc?
A circumhorizontal arc forms when sunlight refracts through horizontally aligned plate-shaped ice crystals in high clouds.
Why do fire rainbows look like burning clouds?
Their intense colors can spread across wispy clouds, making the cloud appear to glow like flame.
Are fire rainbows rare?
Fire rainbows require specific Sun angles, ice-crystal shapes and cloud conditions, so they are less commonly seen than ordinary rainbows.
Are fire rainbows dangerous?
No. Fire rainbows are harmless optical effects caused by sunlight and ice crystals.
