Sun pillars are a phenomenon occurring at sunrise or sunset, in which sunlight appears in the form of flame-like pillars standing perpendicular to the horizon.
On very cold winter days, water vapor suspended in the air freezes to produce “diamond dust”. When the air is still and there is little wind, this falling diamond dust encounters air resistance from below and settles into a horizontal sheet that reflects the rays of the sun to produce a virtual image of sunlight—a sun pillar.