Sun Dogs, Pillars & Mirrors: Optical Phenomena of the Subarctic Sky

What causes them

When the air is cold enough, tiny hexagonal ice crystals float in the atmosphere and bend sunlight in predictable ways, much like tiny prisms and mirrors. Depending on how the crystals are shaped and oriented, that bending produces halos, bright spots, arcs, and columns of light around the sun (or even the moon). Meteorologists have a specific name for the fine ice crystals that cause many of these effects at ground level in extreme cold: diamond dust, a fitting description for something that can turn an ordinary cold morning into a glittering one.

Sun dogs and halos

The most common sight is a pair of bright, often rainbow-tinged spots flanking the sun at the same height, the "sun dogs" (technically parhelia). They frequently appear alongside a 22-degree halo, a luminous ring encircling the sun. Both are best seen when the sun is low and the air is full of ice crystals.

Halos in particular aren't limited to the depths of winter the way sun dogs and diamond dust often are. They form in high-altitude cirrus clouds, which are cold enough for ice crystals no matter what the temperature is on the ground, so a clear day with the right high cloud can produce a halo display even in June. On rare occasions, several halo effects can overlap at once, multiple rings, arcs, and bright spots all interlocking across the sky, producing something far more elaborate than a single ring around the sun. Displays like that are genuinely uncommon and tend to be the ones people remember for years.

Sun pillars and light columns

On very cold mornings and evenings, you may see a sun pillar, a vertical shaft of light rising from the sun as flat ice crystals reflect its glow. In town, the same effect can create eerie light pillars above streetlights, a purely local Yukon winter spectacle.

Mirrors in the sky

The third phenomenon in the sky's repertoire has nothing to do with ice crystals at all. Superior mirages, sometimes called looming, or in their most dramatic form a Fata Morgana, happen when a layer of cold, dense air sits near the ground with warmer air above it, bending light so that distant objects appear lifted, stretched, or duplicated above the horizon. It's a genuine hazard for the unprepared: in 1818, the British explorer John Ross spotted what looked like a mountain range blocking his route through the Arctic and turned his ship around rather than sail on. He named it the Croker Mountains. A later expedition proved they never existed at all, Ross had mistaken a superior mirage for solid land. Temperature inversions like the one that fooled him are a genuinely common feature of Yukon winters, the same cold-air-trapped-in-a-valley setup that also produces ice fog in places like Whitehorse, so the conditions for a mirage here are more common than people assume.

When and where to look

These phenomena favour clear days when ice crystals hang in the air or a temperature inversion has settled in, so deep winter is prime time for sun dogs, diamond dust, and pillars, though halos can turn up anytime a high, thin cirrus layer catches the light. Look toward the low sun (never directly at it, shield it with your hand or an object), and scan for halos, flanking spots, and vertical columns. Around towns, glance up on frigid nights for streetlight pillars.

Capturing them

A wide lens helps fit a full halo in frame; block the sun itself behind an object to reduce glare and reveal the surrounding effects. As with all winter photography, keep batteries warm and be quick, since the crystals, and the display, can shift within minutes.

While the aurora dances at night, the daytime sky has its own quiet magic. Learn to spot sun dogs, halos, pillars, and mirages, and even an ordinary walk, or drive, on a cold Yukon morning becomes a little astronomical event.