lunar fogbow moon bow aurora
LUNAR FOGBOW VS. NORTHERN LIGHTS: Deep inside the Arctic Circle, aurora tour guide Tim Nordström of Abisko, Sweden, routinely sees green curtains hanging down from the sky. On Dec. 28th, he saw something different: a pale arc reaching out of the ground:

"It was amazing," says Nordström. "We were hiking through a frost-covered forest. The air was cold (-25 C) and crisp. At first the fog was thick above us, but after a while it started to thin out so we could see the green auroras overhead. A bright shaft of moonlight lanced through the fog --and that's when we saw the fogbow."

Fogbows are cousins of rainbows and they are formed in essentially the same way: light bounces in and out of water droplets to produce a luminous arc. In this case, the droplets were supercooled (to remain liquid in the freezing air) and much smaller than typical raindrops. Tiny droplets cause a diffraction effect not seen in ordinary rainbows; as a result, the colors are smeared together resulting in a nearly-white arc.

FALSE AURORAS: The space weather forecast did not call for auroras in New Hampshire last night. Yet when Stephanie Graudons of Lebanon NH looked outside at 3 am, the sky was filled with colorful lights. "An unexpected sight," she says, "these light pillars were so amazing that I dragged my fiance out of bed and out into the -14 degree night to photograph them!"

"Shivering in a foot of new snow in a nearby baseball field, we watched until they faded away," says Graudons. "It was well worth the lack of sleep."

Sometimes called "false auroras," light pillars are caused by ice crystals in the air. The crystals' flat faces intercept urban lights and spread them into colorful columns. No solar activity is required for the phenomenon. The only ingredients are ice and light pollution.

The different colors of the pillars are caused by various color temperatures of street lights. Warm orange pillars come from traditional high pressure sodium lamps, while bright white pillars come from newer LED lamps.

light pillars new hampshire Dec 2017
© Stephanie Graudons
December 27, 2017 @ Lebanon, New Hampshire, USA