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date
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2000-10-28:22:13
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Physics
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It's a diversion but I'll comment here on the physics of the aurora.
The aurora borealis and it's austral sibling are caused by high-energy particles from the sun, which are part of the solar wind, exciting gas in the Earth's upper atmosphere. This doesn't happen all the time because the flux of high energy particles isn't constant -- sometimes the sun emits more than at other times. Stars are active -- they have "weather" in their "atmosphere" and the equivalent of hurricanes and earthquakes and more besides. When such events are big enough and pointed the right way, they can spew particles -- mostly protons and electrons -- toward the Earth in abundance.
Because protons and electrons are charged, the Earth's magnetic field acts to deflect them, which protects us from a good deal of radiation. But at the poles the magnetic field is plunging more-or-less straight down into the Earth, which is why compasses work badly at high latitudes. Under these circumstances the particles can spiral down along the lines of the field and impact the upper atmosphere.
What happens next is interesting. As the particles plunge deeper into the atmosphere they run into atoms of oxygen and nitrogen and the like. These collisions transfer energy to the atoms that get hit, which wind up with one or more of their electrons boosted into an excited state. These electrons are like a ball rolling around on a high shelf -- eventually, they will roll off, falling back down to the ground state.
But for the electron to fall down, it has to do something with the energy it's gained. If the excited atom is in a dense part of the atmosphere, then the most likely way for the electron to get rid of its extra energy is to transfer it to another atom during a collision. In a dense gas, atoms are colliding all the time, and when an excited atom runs into another one the excited atom's electrons fall back into the ground state and the other atom gets a little bigger kick during the collision than it expected. It's kind of like when you touch someone who's charged himself up with static electricity by walking on a carpet in stocking feet. This is called "collisional de-excitation."
In a thin gas, like the upper atmosphere, collisions don't happen very often, so another process becomes important. In this process, the excited electron gets rid of it's extra energy by emitting light.
That's what the aurora is. |
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Creatures
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Driving back from Ottawa this evening, in the dark, I saw an owl briefly in the headlights, rearing up from a roadside kill, its great wings flashing white in the staring lights, casting momentary shadows. It was big -- I don't know if we get great horned owls around here or not, but I think it was too big for a barn owl, although it's hard to tell with such a brief view and in such difficult conditions, with nothing close behind it to give a sense of scale.
It reminded me of other owls, at other times, but I'll write about those some other day.
A little further on Jan saw something in the sky, glowing light like clouds illuminated from below, but we were still well north of Smith's Falls, which isn't exactly a major center, and with a cold dry wind still blowing out of the north clouds seemed unlikely. After a bit the glow resolved itself into vertical streaks, and we realized it must be northern lights. This is the first time the kids have seen them, and it was a pretty good display.
They were white, rather than red -- red is rare, at least in my experience -- and stood out in long vertical streaks in the northern sky, coming to within ten degrees of the horizon and reaching as high as perhaps 40 or 50 degrees. As usual, the bottom was cut off in a sharp line, while the top was ragged and streaky.
I pulled off to the side so I could get a look, and then we travelled on, over the dark and lonely landscape. South of Smith's Falls I pulled off again and got out of the car to look again, and could see the galaxy streching across the sky as well. It was a clear night for southern Ontario -- even the Pleiades were clearly visible.
A little further on the aurora faded into a uniform wash, and then vanished entirely in the darkness behind us. I haven't seen them so clearly for many years -- probably not since the summer of 1981, when Sandy and I saw a spectacular display of green that reached down from the zenith in giant fingers like the hand of God, come to unscrew the lid of the sky. Not "rodos", but definitely the "daktylos aurora". |
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Poem
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People like to criticize, and they assume their own superior knowledge. Thus, because I once dared use the phrase "rosey fingered dawn" in a poem, I was told, by someone who assumed I didn't know it, that that phrase "belonged rather famously to Homer." I was thinking about it today because of the experience described in Creatures, and also because something similar happened to me yesterday.
But its the kind of response an artist dreads, like the critic who panned Catch 22 because of the "randomness" of the chapters, when Heller worked so hard to get the look and feel of randomness with an ordering that was very carefully and deliberately chosen. Some people just don't get the joke, and as soon as anyone starts taking those people seriously they stop doing good work -- this is as true in physics as it is in poetry or any other art.
You can't write for your critics, only your Muse. |
