Fire Rainbows Aren't That Rare (Depending Where You Live)

You've probably seen the viral photos: brilliant bands of rainbow color streaking horizontally across the sky, often captioned as "the rarest atmospheric phenomenon on Earth." They're called circumhorizontal arcs, nicknamed "fire rainbows" despite being neither fire nor rainbows. And here's the kicker - they're not remotely close to being the rarest thing in our atmosphere.

The truth is way more interesting than the myth.

Location, Location, Location

If you live in Los Angeles, you could potentially see a circumhorizontal arc on a summer afternoon and think nothing of it. The sun sits high enough in the LA sky for 670 hours between late March and late September - plenty of opportunities for these colorful displays. In the American Midwest and South, they show up several times each summer.

But in London? The sun only climbs high enough for a measly 140 hours between mid-May and late July. In Copenhagen or anywhere north of 55° latitude, they're physically impossible to see. The sun simply never gets high enough.

So "rare" is relative. It depends entirely on where you're standing.

The Recipe for Sky Fire

Circumhorizontal arcs need three things to happen simultaneously:

• The sun must be at least 58° above the horizon (really high)
• Cirrus clouds containing flat, hexagonal ice crystals must be present
• Those ice crystals must be oriented horizontally, like tiny floating dinner plates

When sunlight hits these perfectly positioned ice crystals, it refracts through them at just the right angle, splitting into a horizontal rainbow. The effect can stretch across hundreds of miles of sky when conditions align.

Actually Rare Stuff

Want to talk about genuinely rare atmospheric phenomena? Try the Moilanen arc - so rare that scientists still debate what causes it. Or elliptical halos, which have barely been photographed. Supralateral arcs qualify too, since they require ice crystals with optically perfect end faces, which nature rarely provides.

Even among common halos, there's a hierarchy. The 22° halo (a ring around the sun) and sundogs show up about twice a week in Europe. Upper tangent arcs are fairly common. Circumhorizontal arcs fall somewhere in the middle - frequent enough in the right places, impossible in others.

Why the Myth Persists

The "rarest phenomenon" claim probably stuck because fire rainbows look impossibly rare. They're stunning, photogenic, and unfamiliar to most people. Social media loves a superlative, and "rarest" sounds better than "moderately uncommon depending on latitude."

Plus, for half the planet's population living at higher latitudes, they genuinely are rare or impossible. A Londoner has every right to call them rare - they basically are, from that vantage point.

But atmospheric science doesn't care about vibes. The sky puts on stranger shows than fire rainbows - we just haven't noticed them yet, or we're not standing in the right place when they happen.