It was a frigid morning in Garrett County, Md., when Josh Brenneman encountered an incredible scene on his drive to work.
The rising sun was surrounded by a perfect semicircle of colored light, like a rainbow. But there was no precipitation; instead Brenneman, who runs the Facebook group Allegheny Mountains Weather, was seeing a magnificent ice halo intensified by flanking shafts of light known as sun dogs. The diamond-shaped column of light emanating from the sun itself is known as a sun pillar.
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“[I] first noticed the bright colors on the right side, then when I got to a good open area, the left side was visible and it was only the lower parts at first and slowly built the arch,” he wrote in a message to The Washington Post.
So, how did this scene develop?
Sunlight is made of white light, or a combination of light of all different wavelengths. That means it contains all the colors of the spectrum. When white light enters an ice crystal, the light slows and is bent through a process know as refraction. But each wavelength, or color, of light, is refracted at slightly different angles. That’s what splits up the light into its different component colors, making each unique hue visible to us.
Central to the stunning sky scene is the common 22-degree halo, which can be mistaken for a rainbow. Temperatures were around 15 degrees at the time, which precipitates ice crystals with a hexagonal prism structure in the atmosphere. That crystalline form is perfect for creating a 22-degree halo.
Above and below the sun is a column of light known as a “sun pillar.” Those form when ice crystals take the form of hexagonal platelets and are oriented with their faces pointed up and down. They act as miniature mirrors; any sunlight that is scattered upward is reflected, or bounced, back toward the observer. That generates a vertical beam of light.
To the left and right of the sun anchored on the 22-degree halo are “sun dogs,” or splotches of bright light. These are areas where the ice crystals are oriented with their hexagons facing horizontally, aiming light directly at the photographer. Because blue light is refracted more than red light, the inner edge of the sundog appears tinted red and orange.
Lastly is the parhelic circle, a faint, monochromatic hula hoop at the height of the sun that pierces the solar disk and parallels the horizon. It can be linked to sunlight entering the rectangular sides of a hexagonal prism of ice. Parhelic circles are usually dimmer farther away from the sun because rays of light must take a tortuous path of internal reflections within each crystal.
The four features combined into a serene morning display that appears to have been viewed only locally. Brennan’s brother, a mile away, didn’t report anything unusual or captivating with the sunrise.
There is a chance that the locality of the phenomenon may be tied to snow production at the nearby Wisp ski resort; snow cannons often produce “perfect” ice crystals that lend themselves to the generation of halos, pillars and other colored bands.
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