With the northern lights in the news recently, I was curious how they factored into Norse mythology (if at all). Was there a religious explanation of some sort, or was it merely filed into the same bin as an especially pretty sunset (or something else)?
On mobile, sorry for the formatting.
Based on this Norwegian text ("The Historical Northern Lights") http://munin.uit.no/bitstream/handle/10037/5179/article.pdf?sequence=1
There is disagreement on wether northern lights are mentioned in the Edda. According to some, NL in norse mythology are explained as reflected light from the shields of the valkyries.
The first certain (Norse) mention of NL is in Konungs Skuggsjá (ca 1230 AD). Note that this is after the christening of Scandinavia. It presents three theories:
NL are due to a ring of fire surrounding the seas and the earth, reflected by the ice of Greenland
NL are beams of sunlight refracted through the ice of Greenland (from the far side of the Earth)
NL radiate from ice (glaciers?) due to a power/force in the ice
In addition, there are some "simple" superstitions, bad luck for whistling under NL and things like that.
I'll go with Harald Falck-Ytter's declaration that "Nowhere in the Edda, despite its north European origin, can one find a description of the northern lights...."
Although I believe there's some uncertainty as to whether bifrost, the bridge of the gods, is really a rainbow or something more like the aurora. It's usually described as flaming red, not green, but solar storms might be responsible for the color change. It's not actually described as being in bands of color that I can remember.
The "Viking Answer Lady" isn't all that keen on that explanation, though. She says that because of the shifting of the pole, the aurora probably wasn't pronounced over Scandinavia from 600 to 1600 CE, and that between 800 and 1000, there was a lower-than-average number of sunspots.
I have no idea how great her sources are on that, but it seems reasonable at first glance.