Skinner: Well, that was wonderful. A good time was had by all. I’m pooped.
Chalmers: Yes, I should be goooo-(notices kitchen on fire)-od lord, what is happening in there?
Skinner: Aurora Borealis?
Chalmers: Aurora Borealis? At this time of year? At this time of day? In this part of the country? Localized entirely within your kitchen?
Chalmers: May I see it?
Agnes: Seymour, the house is on fire!
Skinner: No, Mother, it’s just the Northern Lights.
–The Simpsons, episode 22 Short Films about Springfield
Something rare and exciting happened just three days ago in our Solar System. Our Sun, giver of life, heat, light, and energy, experienced a coronal mass ejection.
You can see the “flaring” region in the lower left of the above image. (And get a video here.) But we have another satellite, SOHO, that orbits between the Earth and the Sun, that’s observed many of these Coronal Mass Ejections. Here’s an animation of one from 2001.
Well, on August 1st, 2010, SOHO, SDO, and others noticed a big one — category C3 — ejected from the Sun. (These are typically fairly big.)
In a typical coronal mass ejection, the Sun spits out about a billion tonnes worth of mass, or about as much mass as a large (~1 km diameter) asteroid. (About 10% as large on a side as Gaspra, shown below.)
But this coronal mass ejection was something special. Not because it was larger than most, or brighter, or faster. This one was special because — like many (but not most) CMEs — it was aimed right towards Earth.
Luckily for us, this storm of hot plasma, headed right towards us at 1,000 kilometers per second (or about 100 times faster than any rocket or spacecraft we’ve ever built), has to contend with the Earth’s magnetic field.
The Earth, right now, has its North Pole tilted towards the Sun (and the South Pole tilted away), meaning that nearly all of the charged particles streaming towards us from the Sun were deflected away by our magnetic field, except near the North Pole. (This happens just as frequently when the South Pole is tilted towards the Sun, as shown in the image below.)
The result? The charged particles make it all the way to the Earth’s upper atmosphere, where they collide, producing the beautiful phenomenon known as an aurora!
In the northern hemisphere, it’s known as the Aurora Borealis, while in the southern hemisphere, you get the Aurora Australis. It is, from what I understand, so much more spectacular on a clear night!
Because it’s happening in the upper atmosphere instead of in space, you need to be very far away from the equator to see it. (Like the image below, from Alaska.)
Keen observers in the northern parts of Europe and North America last night, at latitudes above 48 degrees (or so), were able to get some great auroral viewing. Here are some images I’ve managed to find from around the web of last night’s aurora!
Why bring this up today, then, after-the-fact? Because coronal mass ejection often come in pairs, and the second one should hit us tonight! So if you’ve got the opportunity to get up near those northern high latitudes with clear skies, go for it! Do you have any idea of what it looks like over the span of a whole night?