Thursday, September 29, 2011


Jupiter rising

Many cultures thought the aurora to be associated with spirits (among other things, but let's stick with spirits). For example:

  • Some native Canadian and Alaskan tribes thought the aurorae were the dancing spirits of humans or animals.

  • The Vikings thought they were reflections from the shields upon which dead warriors were carried to Valhalla.

  • Labrador natives postulated the aurorae were the spirits of those who died a violent death.

An alien world

  • In east Greenland, it was thought to be the ghosts of children who died at birth.

  • The Fox tribe of Wisconsin thought the aurorae were the ghosts of defeated enemies seeking revenge.

  • The Iroquois thought it was the entry point to the land of souls.

  • The Lakota Sioux turned the whole thing on its head, interpreting the aurora as spirits yet to be born.

Chatanika dredge

Here I've paired the aurora with another kind of ghost, the long-dead machinery of Alaska's gold rush. The Chatanika dredge is an example of the lengths people go to for shiny rocks. In it's heyday, a camp of 10,000 people existed to support its mission of turning over the earth in search of gold. The operation of such a machine left piles of loose rocks, called tailings, three-or-four stories high on both sides of the channel it dug.

Jupiter rising

The rising planet Jupiter, as seen from the base of one of these piles.

By 1960 the dredge was no longer in operation, and it was left to its own devices, to meet its lonely fate under the crisp subarctic sky.

Aurora, clouds, and the old Chatanika gold dredge

"I was amazed at how simple it was for nature to cloak
corruption in the garb of purity and make it peaceful."

- Robert Charles Wilson, Julian Comstock

Monday, September 19, 2011

What is an aurora? Part 1

Aurora over the cabin.

The aurora, more commonly known as the Northern Lights, though they happen in the extreme south too (where they're called Southern Lights, derp), and on other planets as well. But we're Sophisticated People here, and we call them aurorae.

"What is the aurora?" I get asked this question sometimes, and my one sentence gee-whiz answer is 'Electrons from the Sun that hit Earth and make light.' That's a reasonable zero-order explanation, but there's a lot more to it than that, and it's worth learning, because it's interesting.

Anyway, this post will be a big-picture description of what an aurora is. Later, I'll do other posts that describe the details, and add links here when approriate. That makes this the first in a series, which should answer any nagging questions as to why I called this 'Part 1'.

The Earth is a big magnet. That's how compasses work. You ever seen that trick where you stick a magnet near some iron filings, and you get those long curvy lines? Like this:

That happens because the little iron flakes line up along the magnetic field lines, which don't really exist, but no one told the iron flakes. Notice how the lines seem to emerge from the north and south poles of the magnet? Take that long, narrow magnet and make it shorter, rounder, and more Earth-shaped, with the top and bottom where the Earth's north and south poles are, and you get the Earth's magnetic field.

Except it's all lopsided. The Sun keeps spraying it with charged particles (called the solar wind), so it gets all squished up on the side closest to the Sun and stretched out on the other side.

The Sun has its own magnetic field, and the magnetic field lines make lots of loops and twisties. Charged particles like to follow magnetic field lines, so normally they're stuck in those loops. But sometimes one of the loops gets twisted free and thrown off into space, which we call a coronal mass ejection, or CME for short. And when that happens, all the charged particles that were stuck in the loop get thrown off with it. There are roughly equal numbers of positive and negative charges, so they cancel each other out, and the collection of particles is more or less neutral. Because it's awkward to say 'a collection of charged particles which is more or less neutral', we have a special word for it - a plasma. Yes, like your TV.

A CME can get fired off in any old direction, and sometimes they happen to hit Earth. When that happens, we get a substorm. Magnetic field lines get peeled off the edge of the Earth closest to the sun (the dayside), and squish together to reconnect on the nightside. When this reconnection happens, there is a release of energy into the particles that were caught on the field line, and they are guided down to the Earth's upper atmosphere (the ionosphere, specifically) These particles have to follow the field lines, and, if you remember, the field lines come back down into the atmosphere near the poles. Aha! That's why the aurora tends to happen in the extreme north and south - because that's where the magnetic field guides the particles to!

These charged particles come raining down near the poles, and eventually, they bump into an air molecule. When that happens, the air molecule is excited into a higher energy-state, then spits that energy back out in the form of a photon - light. What color photon gets spit out depends on what kind of molecule is doing the spitting. The photons shoot down and hit you in the eyeball, and you see an aurora.

The above explanation will make a lot more sense after you watch these two animations. The first is a CME hitting the Earth, with the field lines reconnecting and funneling particles down to an aurora:

The second shows the particles coming down the field lines and striking air molecules to create light:

And that's the gist of it. Until next time.


Monday, September 12, 2011


Aurora and fall colors

The harvest moon, named for providing enough light for farmers to bring in their crops by night, casts shadows and highlights the contrast between the ephemeral fall brightness of the birch trees and the stubborn evergreen of the spruce. 100 miles up, the aurora forms loops of pink and green before the stars, infinitely higher still, where the ladle of the big dipper tips back precariously, threatening to spill all of a billion years over the landscape, until the silence is broken by the hooting of a nearby owl, pulling me back down to now.

Pink aurora

Saturday, September 10, 2011

It's September...


And the leaves outside are highly yellow. Fall in interior Alaska! The light hitting the yellow leaves and white trunks of the birch trees is very pretty, extraordinarily so when set against a complimentary blue sky:

Yellow Fall Colors

Birch Grove

Up above the treeline, the tundra scrub is a deep red, the likes of which I have never seen anywhere else, with intermixed pockets of yellow:

Denali scenery


Alpine pass


And the sunsets, prolonged by the steep angle of the northern sun, rarely disappoint:

Sunset along the Parks highway

Sunset along the Parks highway Sunset along the Parks highway

It dips below freezing at night now. The days are getting shorter - when I returned to Alaska in July, there was no nighttime; tonight there will be around 8 hours of darkness. The sun is still up for around 45 minutes longer than it is in Arkansas; in two weeks, our daytime will be shorter than that in Arkansas. Our first snow will come soon, and it won't be long afterwards when the lakes and rivers freeze up. After that, we will be firmly in the winter regime - white, dark, and cold. We will be frozen into that state until the end of April, but all of those months are not created equally; Old Man Winter will be noticeably losing his grip on the landscape by the beginning of March. It's just that a Fairbanks winter has a lot of inertia to it, and it takes a while for the springtime sun to pry the land free of the ice.

It has been overcast and rainy for the past few days, and looks like it will continue to be so for the next few. This is disappointing - several CME's are due to strike Earth this weekend, and the resulting geomagnetic storms should make nice aurora viewing, if only we could see through the cloud layer. C'est la vie.

Saturday, September 3, 2011

Fall Colors - Sky

Down the road

Caught my first aurora of the season on the night of Aug 28-29. It was already beginning to break up when I noticed it and came outside, so I didn't get to see the highly ordered/structured period. Breakup is a time when the aurora gets more chaotic and disintegrates to a diffuse glow with little or no structure.

A mess

Aurora season is here Satellites and aurora

In the trees

Under a blanket of green

Fall Colors - Ground


Some early-fall colors, above the treeline on Rainbow Ridge in the Alaska Range.

Tundra vegetation

Fall colors above the treeline High altitude tundra vegetation

And a Willow Ptarmigan heading for a quieter locale, away from the two humans that disturbed it:

Ptarmigan in flight

You can see more pictures (including some of Yours Truly), and read about the hike, in Lee's entry. He says:
I think we both expected more of a "trail" here, but after searching for and failing to find an elusive cairn described by the book we just took off in an upward direction.