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.

Star trails and aurora

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.

Like a bullet through an apple

This:

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.

(Source)

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.

(Source)

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.

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

Ghosts

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.

• 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.

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.

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.

"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