![Some more about the earthly aurora, and what sounds it might make.
Sadly, the northern lights aren’t portals to other universes, like in His Dark Materials. One early attempt at explaining them as a natural phemonenon, rather than a manifestation of the spirit world, is found in Konungs skuggsjá, a Norse text from around 1250 written as a textbook for the Norwegian prince Magnus Lagabøte. The text describes northern lights on Greenland and puts forth several hypotheses. One goes “that the frost and the glaciers have become so powerful there that they are able to radiate forth these flames [i.e., the aurora].” Around 1900, Kristian Birkeland sought to explain the nature and distribution of the aurora around the poles by building a magnetized sphere modeled on the Earth, a terrella. He put the model in a vacuum chamber and directed a beam of electrons at it, observing an aurora-like effect around its poles.
Birkeland thought the electrons came from the Sun, as northern lights were observed in conjunction with solar activity. As you may be aware, we now know that the aurora is triggered by the solar wind, but is caused by interactions within our upper atmosphere. Protons and electrons flow out of the Sun and, under the influence of Earth’s magnetic field, which flows into and out of the magnetic poles, these particles crash into and excite oxygen and nitrogen 50 miles above our heads. Electrons within the oxygen or nitrogen atoms become “excited”, i.e., elevated to a higher energy state, but they quickly fall back to their original state, and the excess energy becomes a photon. In aggregate, this produces the light we see as the aurora. Oxygen atoms emit green and brownish-red light; nitrogen emits blue or red.
But does it make sound? There is a sound associated with the aurora. However, there’s a whole lot of anecdotal data and no recordings. If you’ve ever seen the aurora, you may have heard this sound—or you may not have. (Personally, I have seen the northern lights many times, but never noticed any distinct sound.) But many people claim to have heard a rustling or crackling or static-y sound on cold, clear nights when the aurora dances over the wilderness. And if this can’t be chalked up to overactive imaginations, something must be behind it. It remains unlikely that actual sound could be carried down from the upper atmosphere, where air is spread out thin. It just might come down to radio waves:Of all the hypotheses, the most likely suspect, since it can be duplicated in the lab, is electrophonic transduction. Certain very low frequency radio waves have the same frequency as sound waves. Long, thin conductors – grass, hair, wire eyeglass frames – serve as antennae for these radio waves. When these antennae receive the signal, they vibrate and transform the radio energy directly into sound.
VLF radio waves have been detected in aurora displays, and have been found to be produced by meteors as well. It is worth noting that sounds similar to those associated with aurora have been heard in conjunction with meteors, and even recorded.
More about the aurora: images extrapolated from satellite data, for the southern and northern hemisphere. Use them to see where the northern or southern lights may likely be seen right now. Image credit: northern lights over Greenland, by Nick Russill.](http://25.media.tumblr.com/tumblr_lp1ny9dJbq1qzo4mso1_500.jpg)
Some more about the earthly aurora, and what sounds it might make.
Sadly, the northern lights aren’t portals to other universes, like in His Dark Materials. One early attempt at explaining them as a natural phemonenon, rather than a manifestation of the spirit world, is found in Konungs skuggsjá, a Norse text from around 1250 written as a textbook for the Norwegian prince Magnus Lagabøte. The text describes northern lights on Greenland and puts forth several hypotheses. One goes “that the frost and the glaciers have become so powerful there that they are able to radiate forth these flames [i.e., the aurora].” Around 1900, Kristian Birkeland sought to explain the nature and distribution of the aurora around the poles by building a magnetized sphere modeled on the Earth, a terrella. He put the model in a vacuum chamber and directed a beam of electrons at it, observing an aurora-like effect around its poles.
Birkeland thought the electrons came from the Sun, as northern lights were observed in conjunction with solar activity. As you may be aware, we now know that the aurora is triggered by the solar wind, but is caused by interactions within our upper atmosphere. Protons and electrons flow out of the Sun and, under the influence of Earth’s magnetic field, which flows into and out of the magnetic poles, these particles crash into and excite oxygen and nitrogen 50 miles above our heads. Electrons within the oxygen or nitrogen atoms become “excited”, i.e., elevated to a higher energy state, but they quickly fall back to their original state, and the excess energy becomes a photon. In aggregate, this produces the light we see as the aurora. Oxygen atoms emit green and brownish-red light; nitrogen emits blue or red.
But does it make sound? There is a sound associated with the aurora. However, there’s a whole lot of anecdotal data and no recordings. If you’ve ever seen the aurora, you may have heard this sound—or you may not have. (Personally, I have seen the northern lights many times, but never noticed any distinct sound.) But many people claim to have heard a rustling or crackling or static-y sound on cold, clear nights when the aurora dances over the wilderness. And if this can’t be chalked up to overactive imaginations, something must be behind it. It remains unlikely that actual sound could be carried down from the upper atmosphere, where air is spread out thin. It just might come down to radio waves:
Of all the hypotheses, the most likely suspect, since it can be duplicated in the lab, is electrophonic transduction. Certain very low frequency radio waves have the same frequency as sound waves. Long, thin conductors – grass, hair, wire eyeglass frames – serve as antennae for these radio waves. When these antennae receive the signal, they vibrate and transform the radio energy directly into sound.
VLF radio waves have been detected in aurora displays, and have been found to be produced by meteors as well. It is worth noting that sounds similar to those associated with aurora have been heard in conjunction with meteors, and even recorded.
More about the aurora: images extrapolated from satellite data, for the southern and northern hemisphere. Use them to see where the northern or southern lights may likely be seen right now. Image credit: northern lights over Greenland, by Nick Russill.
dailymeh posted this on July 28, 2011
