Last night we were hibernating. Rosie’s friend K was over and they were baking cookies. I was trying to stay out of the way while still having a good time. At 8:45 someone, we think it was our friend Wrench, made a very garbled cell phone call to us telling us that you could see the northern lights right then.
We live in the very middle of the Twin Cities. It is not the kind of place one associates with seeing the aurora borealis. One time last year, they were visible all over the city and it blew me (and a lot of people) away. I’d only seen them at this latitude one other time and that had been by the river in Stillwater, a much darker night sky.
Anyhow, the three of us stepped out on the balcony last night and sure enough, strange bands of light speared the orange night sky, mostly in the west and north. I snapped some photos, with mediocre results.
They were strange northern lights, but when aren’t they? It didn’t seem likely on this hazy night, but what else could it be?
As usual, you should never just dismiss questions like that. With a little bit of poking around, it turns out that what appeared in the Minnesota sky last night was not the aurora borealis, but “light pillars.” They’re cousins of such phenomena as sun dogs.
Pillars appear in the sky when snow or ice crystals reflect light forward from a strong source such as the sun or moon. Those crystals with plate or column shapes provide an excellent surface from which the light may reflect toward the viewer’s eyes. Ice crystals in the form of plates or columns can be found in ice clouds (cirrus or alto forms), ice fogs, snow virga falling from high-based clouds, blowing snow and diamond dust.
Because the light rays forming pillars are reflected, they take on the colour of the incident light. For example, when the sun is higher in the sky, pillars are white or bright yellow in colour. But when it is near the horizon and its light colour dominantly orange, gold or red, so is the resulting pillar.
Last night’s lights were most likely actually caused by the redirection of streetlights or other bright lights in the city. Surreal that the city can create an appearance like that, mimicking and competing with brilliant natural occurences.
The coolest thing in my rudimentary understanding of light pillars is that they form when long and skinny ice crystals are falling so slowly through a very still atmosphere that they all align so that they are parallel to the earth. Thinking about it, I derive a strange, calm sense of mysterious order.