Q & A about last night.
What happened??? Why didn’t we see a great aurora last night further south that usual?
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There was an event on the sun. A sunspot region threw a X1 class flare. It was a big flare, and nice to see because it has been awhile since we saw one, especially headed toward earth (the term for this is “geoeffective”). This is called a coronal mass ejection or CME.
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What is a “hit”? This is when the particles from the flare (the CME) will be detected on the satellite. I do not think this is an official term.
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After it hits, when will we see the aurora? The particles now have to travel from the satellite into earth’s atmosphere. Depending on the speed will determine when it will arrive. It can be really fast with a big storm, less than a hour. Or an hour or longer. “Typical” or “background level” aurora can be seen during this time while we wait. Many might think “this is it!”, but it is not. We wait for the big event!
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Even when it hits, we still need the IMF to be in alignment. We still need that negative Bz. A powerful storm with very high solar winds can push particles thru despite, and you may still see aurora. Also, between the satellites and the earth there is a big space. In that space, the direction and strength can change. This is why when the data is terrible, we might still see aurora, or when the data is great, and there is no aurora.
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So enough with the science….why didn’t we see aurora down in *Insert state*? You did not see aurora because the CME was apparently weaker than the scientists thought, or, the direction of the CME was not a direct slam.
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Why did the news media tell me there was going to be a big show? I don’t know, maybe because the forecast was Kp 7 and the news media is hung up on Kp levels. Or maybe because the X1 flare is exciting and could’ve produced a nice show. Many of the maps I have seen drawn for Kp 7 were very generous! Also, big cities with giant light pollution blooms almost never can see aurora. Any photos you might have from a big city, compare streetlights of that year to the current light pollution and you might understand why I say this often.
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How often does this occur? Many times per year. I would say only half the time the news picks up on it.
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I sat in my car all night long for nothing. Why did you say to wait sunset to sunrise? We say AFTER the CME hits is when to start the wait in place. Before the CME hits is when to prepare your trip if traveling far, or to charge your camera batteries. You do not start charging batteries when the CME hits. Be ready. It is hard to plan a long driving trip to see aurora when a CME is forecast. A lot of the time the timing is off. It almost NEVER is on time, and those articles or people that tell you “the best time” or the “peak” are wrong! Ignore those people! You can only know the “peak” after the event is over.
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Should I try again? Yes, every time, it is worth it when you see it hit earth. Next time though, do not drive and sit there in the dark for hours without knowing the data, and or without knowing it hit. The exception is, if you have no internet to look it up, enjoy your night time excursion. The night sky is an amazing experience. For typical aurora, which is seen practically every night inside the aurora oval, it is ok to sit and wait. We wait for the earth to rotate, and the IMF to be in alignment.
This CME, as it collides with earth’s magnetic field, may produce auroras. In order for this to happen, it needs to be in the correct orientation. Now to know the details, we look at the numbers for the Interplanetary Magnetic Field, or IMF. The IMF includes the Bt (strength) and the Bz (direction). We want the Bt to be high, and the Bz to be negative.
A negative Bz can be referred to as southward. We want a negative or a southward Bz. This indicates that the particles are being pushed into earth’s magnetic field, and therefore producing aurora.
We also watch the solar wind speeds. With an incoming CME, the speed will rise. On the chart, you may see a blip, a sharp rise, or a stair climb of sorts…you will see it move as you watch minute by minute or check on it every hour or so. Each event might look slightly different, which is why many hobbyists will wait to declare the CME a “hit”. Sometime we like to wait for a pro to declare it! No shame in that.
How can you learn more? Here are my favorite websites and people to follow
List of who I follow on Twitter
Have a great night!
by Amy Stratman