Saturday, October 29, 2011

October 24 Aurora


I took this on Monday, when a coronal mass ejection (CME) collided with the Earth's magnetic field. This, in itself, is not out of the ordinary. What is abnormal is for the effects to be seen so far down south. The resulting geomagnetic storm had auroras visible from Arkansas - I had a friend in my hometown call and ask 'Why's the sky red like that?' I, of course, had no clue what he was talking about, and suggested dust or thin clouds lit up by the sunset. :P

From Ontario, it looked like this:

Ozark, AR had yet another view:

It was big news, since this was a brand new experience for most people down there - I must admit, I flipped shit myself when I saw my first aurora last September, and it can still stop me in my tracks, even after seeing countless more.

But those of you who saw it, or even just saw pictures, may be wondering: why didn't it look like the auroras you see in the pictures I take? Well, for one, you're looking at it out on the horizon. Being lucky enough to live under the auroral oval means they're much higher in the sky for me, and consequently much closer. There are advantages to having your aurora overhead*. One is that it's easier to tell the structure - imagine trying to figure out the folds in a curtain from the side compared to looking up from the bottom. Another advantage is that your line-of-sight through the aurora is longer (optical path length) and so the aurora appears brighter.

[*Actually, what matters in both of these cases is not necessarily having the aurora 'up' so much as having it near the magnetic zenith; but for those of us living in the far north, that roughly corresponds to overhead.]

Overhead Aurora

Perhaps more importantly, strong magnetic storms (required to bring aurorae that far south) tend to have auroras dominated by high-altitude reds, which are in a thinner part of the atmosphere - consequently, the aurora produced looks thinner. More normal levels of magnetic activity tends to produce auroras dominated by a lower-altitude green. These occur in a much lower and denser part of the atmosphere, which makes them look more substantial and structured. For example, this timelapse I filmed a few weeks ago:

Compare to this timelapse shot from Ozark, AR on the 24th:

Which is a roundabout way to saying: All aurora sightings are not equal, there are a variety of colors, shapes, and motions for us to explore.

Thursday, October 20, 2011


Falling snow

It stays below freezing most of the time now, and the snow has arrived. At first, only a few intrepid pioneers wafted down to stake their claims among the fallen leaves.

First flakes

Soon the white invaders were arriving in earnest.

Falling snow Falling snow

After that, it didn't take long for everything to be draped in white.

Snowy cabin Snowy trees

The first snow brings a sense of inevitability - it's coming. But there is an excitement carried along with that, with a tinge of danger that makes it all the more intoxicating. People from outside often wonder why someone would want to live in a place where it can go for 2 months without ever rising above 0ºF. Why don't you come see for yourself? It's mostly indescribable. Already there are hints of the special beauty this place has in winter - the mirages on the mountains, the pillars and halos around the sun and moon, the crisp night skies, the light gradients and soft colors you only notice when all other colors are gone. A month from now, those hardy enough to brave the temperatures will be rewarded with a world reduced to fluffy white outlines, delicate fractals of ice hanging anywhere moisture is present, and sunrises that merge with sunsets to create a single four-hour long spectacle of shadow and light.


Yeah, yeah; so it gets cold. To surrender all this because wearing gloves and a coat is too inconvenient? Madness...


Twigs and reflections

From a night hunting auroras along water features, almost two weeks ago. I think all the still water is frozen now, so no more of this type of shot until next fall. Enjoy.

Thursday, October 6, 2011

Star trails and aurora

Aurora star trails

The planet Jupiter fleeing with the rest of the stars ahead of an auroral arc.

This is my first attempt at star trails. Not bad for a first try! It's a composite of many 30 second exposures. The sky was clear when I started, then the aurora showed up to make things greener. Jupiter is the bright thing, and the Pleiades cluster is just about to disappear behind the tree just left of center.

Monday, October 3, 2011

Like a bullet through an apple


is awesome. The disk in the middle is a coronagraph: a thing used to block out the bright sun so the dimmer things nearby can be seen. So it marks the location of the sun, and lets us see the sun's corona (bright streamy stuff). Coming in from the lower right is a comet. It was discovered by amateur astronomers on Friday. The next day, it disintegrated as it approached the sun. It disappears behind the coronagraph, making it appear to hit the sun. Shortly afterwards, a coronal mass ejection (CME) bursts out of the opposite side. This is probably a coincidence. What is definitely not happening is the comet smashing into the side of the sun and knocking a big hole out the other side, which is exactly what it looks like.

As a side note, you can identify a few coronal features here. The bright pointy loopy thing on the lower left is called a helmet streamer, it marks the location of the current sheet separating the upper half of the sun's magnetic field from the lower half.

And the dark areas, where it doesn't look like anything is coming out, are coronal holes, which are places where the field lines are 'open'. A closed field line is one that loops back in to connect to itself, whereas an open line goes off forever.

Magnetic field lines can't really be open (by the zero divergence Maxwell's equation), but in this case the lines loop so far off into the void before they come back to close that we don't know or care what they do out there: for practical purposes, they're open. It's just that the 'open' lines coming out of one hole are the same 'open' lines that come back in another hole.

05October2011 edit: Astronomy Picture of the Day is now covering this, see here.