Have you ever looked up at the sky and seen a column of light hanging directly below the sun, as if the sky itself had lit a candle? That is precisely what residents across Austria witnessed, and the footage they captured has been spreading rapidly across social media, leaving viewers baffled.
A Spectacular Atmospheric Phenomenon
What they were looking at is known as a subsun, or “sun candle”, one of the most visually striking optical phenomena the atmosphere has to offer. While it may look otherworldly, the science behind it is a story of ice crystals, geometry, and light doing what it does best: the unexpected.
Here are some of the most spectacular videos from X.
So, What Exactly Is a Subsun?
A subsun is a bright, roughly oval patch of light that appears directly below the sun. The phenomenon occurs when sunlight bounces off millions of tiny, flat ice crystals suspended in the air. These crystals (known as plate crystals) drift with their flat faces oriented almost perfectly horizontal, like microscopic mirrors floating in formation. When sunlight strikes them at the right angle, they collectively act as a giant, slightly wobbling mirror in the sky, reflecting the sun’s image downward toward the observer’s eye.
The result is a glowing patch of light that sits below you — or, more accurately, below the horizon as you perceive it.
The subsun is most commonly seen from elevated vantage points: mountain peaks, aircraft windows, or tall buildings. From ground level, the reflected image falls beneath the visible horizon and simply cannot be seen. The higher you are, the more of the sky opens up below the horizon line, and the more likely you are to catch this atmospheric sleight of hand.
Why Does It Look Like a Candle or Pillar?
If the subsun is simply a reflection, you might expect it to look like a clean, circular copy of the sun. So why does it so often appear as a tall, wavering column of light, more flame than mirror image?
The answer lies in imperfection. In an ideal world, every ice crystal would float with its flat face perfectly horizontal. The reflection would then appear as a sharp, compact disc. But the atmosphere is not a controlled laboratory — the crystals tilt, wobble, and drift as they descend, and those tiny deviations stretch the reflection vertically into the elongated, shimmering shape we recognise as the sun candle.
Think of sunlight glinting off a gently rippling lake. A perfectly calm surface gives you one sharp reflection. Introduce the faintest breeze, and that single point of light stretches into a long, dancing streak. The subsun works on the same principle, only the rippling surface is not water, but millions of microscopic ice crystals suspended high in the frigid air. As they shift and rotate, brief pulses of brightness ripple through the column, giving it that living, flickering quality that makes it look far less like an optical trick and far more like something that glows from within.
Can You Spot One Yourself?
Austria’s alpine terrain makes it a natural hotspot for subsun sightings. The country’s abundance of mountain peaks and ski lifts puts observers high above the valley fog and freezing air where plate ice crystals tend to form. Those sightings were aided by the cold, settled winter weather that has been gripping Central Europe. It created perfect conditions for the flat, horizontally-drifting crystals on which the phenomenon depends.
If you want to catch one yourself, the recipe is simple. Find some height, wait for a cold and hazy winter day with thin cirrus clouds or freezing fog below you, and position yourself with the sun low in the sky ahead of you. An aircraft window seat on a sunny winter flight is, statistically, one of your best chances. Look down and forward toward the sun’s reflection, and if the conditions are right, the sky just might light a candle for you!