Yesterday, before dawn, an icy fog rolled in. Most of it dissipated as the sun rose. High cirrus cloud remained. The result was the glorious phenomenon known as Sun Dogs (or Parahelia). It wasn't bitterly cold, as is usually the case when we see Sun Dogs here.
Sun dogs happen when sunlight passes through ice crystals in the air. The ice crystals are flat hexagonal in shape and act as prisms, bending the light rays at 22°. If the crystals are randomly aligned in the air, the 22° Halo forms. If the crystals are aligned horizonally as they fall, the refracted light is concentrated into Sun Dogs.
I'll turn it over to The Weather Doctor who explains:
"
Ice crystals in the atmosphere are hexagonally shaped. Crystals forming most optical phenomena in the air are typically hexagonal rods, shaped like pencils, or flat, hexagonal plate patterns, like microscopic stop signs or dinner plates. When plate-shaped ice crystals fall unimpaired, drag forces automatically orient them horizontally so that their larger, flat surface parallels the earth like a large maple leaf drifting down from a tree.
Sun dogs emerge when sunlight passing through the ice plate's thin sidefaces is refracted. The more perfectly aligned the falling crystals are to the horizontal, the more compact the resulting sun dog. Crystal misalignment from true horizontal will spread the sun dog vertically — its angular height being approximately four times the maximum crystal angular tilt.
Sun dogs frequently display a reddish tint on the side facing the sun and may sport bluish-white tails which stretch horizontally away from it. The degree to which colours are visible depends on the amount of wobble in the ice crystal's fall: the more wobble, the more colour. The sun dog's tail is formed by light passing through the crystal at angles other than the optimal deviation angle."
A second bit of refraction is happening at the horizon from air-bourne snow crystals - the colours are just visible to the left of the trees in the photo below
High Noon and Due South at the 49th Parallel on December 25, 2010
Auspicious times to come? Throughout the ages, people have ascribed omens and portents to the appearance of Sun Dogs. Wikipedia has a collection of associated past events.
Sun dogs happen when sunlight passes through ice crystals in the air. The ice crystals are flat hexagonal in shape and act as prisms, bending the light rays at 22°. If the crystals are randomly aligned in the air, the 22° Halo forms. If the crystals are aligned horizonally as they fall, the refracted light is concentrated into Sun Dogs.
I'll turn it over to The Weather Doctor who explains:
"
Ice crystals in the atmosphere are hexagonally shaped. Crystals forming most optical phenomena in the air are typically hexagonal rods, shaped like pencils, or flat, hexagonal plate patterns, like microscopic stop signs or dinner plates. When plate-shaped ice crystals fall unimpaired, drag forces automatically orient them horizontally so that their larger, flat surface parallels the earth like a large maple leaf drifting down from a tree.Sun dogs emerge when sunlight passing through the ice plate's thin sidefaces is refracted. The more perfectly aligned the falling crystals are to the horizontal, the more compact the resulting sun dog. Crystal misalignment from true horizontal will spread the sun dog vertically — its angular height being approximately four times the maximum crystal angular tilt.
Sun dogs frequently display a reddish tint on the side facing the sun and may sport bluish-white tails which stretch horizontally away from it. The degree to which colours are visible depends on the amount of wobble in the ice crystal's fall: the more wobble, the more colour. The sun dog's tail is formed by light passing through the crystal at angles other than the optimal deviation angle."
High Noon and Due South at the 49th Parallel on December 25, 2010
Auspicious times to come? Throughout the ages, people have ascribed omens and portents to the appearance of Sun Dogs. Wikipedia has a collection of associated past events.
