Alaska’s extreme cold and long hours of low winter sun make it one of the best places in the country to see a family of atmospheric optical effects known as ice halos, including sun dogs, the 22-degree halo, and light pillars. These displays are sometimes described locally with informal nicknames, but they are well-documented, real phenomena with a straightforward scientific explanation, not a mysterious or unnamed occurrence.
What causes them: All of these effects come from sunlight (or moonlight) passing through tiny hexagonal ice crystals suspended in the atmosphere, either in high, thin cirrus clouds or, on very cold days, in “diamond dust” ice crystals floating near ground level. As light enters and exits these crystals, it bends and separates by wavelength in much the same way a glass prism splits light into colors, producing rings, arcs, and bright spots of light around the sun.
Sun dogs: Also called parhelia, sun dogs appear as bright, sometimes colorful spots of light to the left and right of the sun, at the same height above the horizon. They form when sunlight refracts through flat, plate-shaped ice crystals that are falling with their faces roughly horizontal. Sun dogs are most vivid when the sun is low in the sky, which is why they’re especially common during Alaska’s winter, when the sun never climbs far above the horizon even at midday.
The 22-degree halo: This is a faint, often colorless ring that circles the sun (or moon) at a fixed radius of 22 degrees, roughly the width of an outstretched hand at arm’s length. It forms when light passes through randomly oriented ice crystals in cirrus clouds, and it’s one of the most common atmospheric optics displays anywhere in the world, though Alaska’s cold, crystal-rich air produces it especially often and vividly.
Light pillars: On very cold, calm nights or mornings, especially in interior Alaska around Fairbanks, artificial or natural light can reflect off falling ice crystals to create a vertical column of light stretching above (or below) its source. Streetlights and the rising or setting sun are common sources, and the effect is easiest to see when temperatures drop well below freezing and the air is still.
When and where to look: Interior Alaska, including Fairbanks and the areas around Denali, sees these effects more often than coastal cities like Juneau or Ketchikan, because cold, dry, still air is more likely to hold the ice crystals needed to produce them. Winter mornings and late afternoons, when the sun sits low on the horizon, are the best times to look. Unlike the aurora, which requires clear dark skies at night, these ice-crystal effects are a daytime phenomenon and don’t require any special viewing conditions beyond cold weather and a bit of moisture in the air.
Photography tips: Because sun dogs and halos form around the sun itself, use a lens hood, your hand, or an object like a building or tree to block the direct sun from hitting your camera sensor, which both protects your gear and makes the halo or sun dogs easier to see in the resulting photo. A wide-angle lens helps capture the full 22-degree halo, since it spans a wider arc of sky than it might appear to the naked eye.
These ice-crystal displays are a reminder that some of Alaska’s most striking natural phenomena don’t require a wildlife sighting or a glacier cruise to experience, just cold air, a little patience, and a glance toward the sky on a clear winter day.
