Why Winter Sometimes Brings a "Rainbow" — and How It Differs From the Familiar Summer One

A frosty morning, clear sky, not a cloud in sight — and suddenly a glowing ring flares up around the sun. Or two rings. Or two bright spots appear beside the sun, looking like its twins. It looks like a glitch, but it's entirely real physics.

Spotting something rainbow-like in winter, people usually grab their phone, take a photo, and caption it "a rainbow in winter, what a miracle." In reality, winter skies can produce two fundamentally different phenomena — and it's worth telling them apart, since they form differently, look different, and even predict different weather.

Can an Ordinary Rainbow Appear in Winter?

Yes, though rarely. A classic rainbow forms when light refracts through raindrops, and it requires two conditions: rain (or at least airborne water droplets) and sunlight shining from behind the observer.

In winter, this combination becomes possible during a thaw: the temperature climbs above freezing, rain or sleet falls, the sun peeks out — and an entirely ordinary seven-color arc appears in the sky, indistinguishable from a July rainbow.

But this doesn't happen often — a thaw with simultaneous rain and sunshine coincides only a handful of times per winter in central Russia.

What People Actually See in the Cold

Far more often, what gets called a "winter rainbow" is an entirely different phenomenon: a halo. This is a glowing ring, arc, or scattering of bright spots around the sun, formed not in water droplets but in ice crystals suspended in the air.

Galina Sheporenko, chief meteorologist for Sverdlovsk Oblast, explains that in severe cold, the air fills with tiny hexagonal ice crystals invisible to the naked eye. Sunlight passing through their facets refracts and scatters, producing the rainbow-like shapes that appear in the sky.

How a Halo Differs From a Rainbow

The difference goes beyond the name. Rainbows and halos are structured in fundamentally different ways, and you can tell them apart at a glance.

• Position in the sky. A rainbow always appears opposite the sun — you stand with your back to it and see the arc in front of you. A halo, by contrast, surrounds the sun itself — you're looking directly toward it.
• Color order. A rainbow shows red on the outside, violet on the inside. A halo runs the opposite way: the red edge faces the sun, while the outer edge fades into a washed-out white glow.
• Brightness and palette. A summer rainbow displays all seven colors, vivid and saturated. A halo tends to be paler: reddish and orange tones dominate, while violet and blue are barely distinguishable.
• Shape. A rainbow is always an arc (part of a circle). A halo can take the form of a ring, an arc, a cross, a vertical pillar, or even a pair of bright points flanking the sun.

Which Forms of Halo You Might See

Scientists have cataloged over a hundred types of halo, but a few show up most often in everyday life.

• The 22-degree ring — the most common form: a glowing circle around the sun with an angular radius of 22°. It looks like a pale rainbow-colored circle, with the sky inside it appearing slightly darker than outside.
• Sun dogs (parhelia), or "false suns" — two bright, rainbow-colored spots to the left and right of the sun, exactly at the horizon level. Sometimes bright enough to make it look like three suns hang in the sky at once.
• Light pillars — vertical beams of light extending upward (and sometimes downward) from the sun. These form when flat crystals drift slowly and horizontally through the air, acting like tiny mirrors.
• The circumzenithal arc — a bright, rainbow-colored "smile" high overhead, curving away from the sun. Rarer, but its color saturation can rival that of a summer rainbow.

When and Where the Odds of Seeing a Halo Are Highest

Three conditions need to align: freezing cold, high humidity, and bright sunlight. Crystals form either in cirrus clouds at 5–10 kilometers altitude, or right near the surface — in so-called "diamond dust," when microscopic ice needles hang suspended in the air and shimmer in the light.

In central Russia and the Urals, halos are most commonly observed December through February, especially on clear, frosty days following snowfall. In Siberia and the Far East, where frosts run harsher and air stays drier, "diamond dust" is nearly commonplace, and halos can appear several times a winter. In the Arctic, they occur regularly.

What a Halo Tells You About the Weather

The appearance of a 22-degree ring around the sun is one of the oldest folk weather predictors — and in this case, the folk wisdom lines up with the science. The cirrus clouds whose crystals produce the halo often travel ahead of a warm atmospheric front. Within a day or two of seeing a ring around the sun, a warm-up often follows, trailed by precipitation.

In winter, this works as a genuine reference point: spot a halo in the cold, and there's a real chance temperatures will rise within a day or two, bringing snow. Not a guarantee, but the correlation holds up noticeably more often than chance would predict.

Can You See a Halo at Night?

Yes — around a full moon. The principle is the same: moonlight refracts through ice crystals in cirrus clouds, producing a pale ring around the moon. The colors in a lunar halo are barely distinguishable — the light is too faint for a full spectrum — but the ring itself is clearly visible.

The folk prediction is the same one: a ring around the moon signals a coming change in weather and precipitation.

How to Tell One From the Other in Three Seconds

If the glow sits opposite the sun and looks like a colored arc, that's a classic rainbow, even a wintertime one. If the glow surrounds the sun or sits near it as a ring, a pillar, or bright twin spots, that's a halo.

Both phenomena are harmless to look at in the sense that they don't cause damage on their own, but staring directly at the sun to photograph a halo is a bad idea in any season.