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.

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