GRACEVILLE, Minn.-- A bitterly cold morning in Minnesota made for a spectacular scene in Graceville on Monday.
Carol Bauer was out around 5:30 a.m. when she spotted dramatic light pillars and a moon dog in the pre-dawn skies.
The displays are caused when the air is moist, but so cold, it's full of tiny ice crystals instead of water droplets. In this case, the temperature was around 1 degree with recent light snow, and the air remained nearly saturated.
For the shining vertical columns to form, the crystals' shape refracts the light from the ground, appearing as a tall, luminous pillar stretching skyward from the light source.
The ice crystals need to be about halfway between your eyes and the light source for effect to take hold. The pillar's height depends on how high the crystals are positioned and your distance from the light source.
Higher crystals and/or closer light sources will create taller pillars.
The "moon dogs" -- similar to sun dogs -- are two sources of light directly to the left and right of the moon, sometimes known as "mock moons."
LEARN: What is a Sun Dog?
They're formed when you have more orderly ice crystals, according to Michael Kavulich, a research scientist with the National Center for Atmospheric Research.
In this case, we have what is known as plate crystals that are six-sided shapes with flat tops but have some thickness to them.
"So it's kind of like a dinner plate, and those actually tend to fall slowly-- almost kind of fall straight down like a leaf," he said. "And since that angle (of refraction) is 22 degrees, you see two bright spots on either side of the (moon)," he said.