Of Particular Significance

Northern Lights Tonight?

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 04/13/2013

[UPDATE, midnight New York time: the cloud of particles from the solar flare arrived a few hours ago, but it didn’t impact the earth’s magnetic field quite as hard as the best-guess forecast. (Remember the probability of a geomagnetic storm was only 60%; i.e. the probability of no storm was 40%.) Right now, the auroras are likely visible in Canada but probably not in the US. This could change, but don’t get your hopes up too high; we may have to wait for the next solar flare.]

I’ve been sidelined with computer troubles and non-science activities, so first, a belated thanks to everyone who left a thoughtful comment after Monday’s post and question about communicating science to the public.  I appreciate hearing your views, especially from readers with a diversity of backgrounds!

Now, many of you may have heard that there is a forecast of northern (and southern) lights, also known as auroras, tonight.  What you’ve heard is correct: today’s NOAA space-weather forecast, from  http://www.swpc.noaa.gov/forecast.html,  says

VI.  Geomagnetic Activity Probabilities 13 Apr-15 Apr
A.  Middle Latitudes
Active                30/30/15
Minor Storm           35/45/05
Major-severe storm    10/15/01
B.  High Latitudes
Active                10/15/15
Minor Storm           20/25/20
Major-severe storm    60/35/20

i.e. it shows that even in mid-latitudes (meaning northern US and southern Canada, and northern Europe, along perhaps with parts of Australia and New Zealand [?]) they are estimating a 35%-45% probability of a minor `geomagnetic storm’ tonight, with a 10-15% probability of a major storm… and a geomagnetic storm, which literally means a lot of activity in the earth’s magnetic field, generally leads to auroras further away from the north and south pole than usual.

Auroras are caused when swarms of electrically charged particles (electrons and ions) from the sun arrive in the earth’s vicinity, are captured by the earth’s magnetic field, spiral down toward the north and south pole of the earth, and hit molecules in the earth’s atmosphere, causing them to glow.  [Here’s a NASA flyer with a drawing and a little more information.] A strong solar flare (a giant explosion on the surface of the sun) can generate a huge cloud of charged particles (a CME, or coronal mass ejection), and if this cloud arrives at the earth it can not only generate auroras but also move the earth’s magnetic field around, with the effect that some of this glow is found well away from its usual location near the poles, over places where more humans live.

And because there was a big CME on Thursday that seemed to be aimed at the earth, and because it takes about two days for such a cloud to travel out to where the earth is, the space weather forecasters are expecting the CME’s particles to hit the earth any time now It has apparently arrived! When that happens, if enough of those particles get caught in the earth’s magnetic field, we’ll start seeing auroras away from the earth’s poles.

Auroras are generally quite dim, though easy to see in a naturally dark sky — so you need to be looking after dark and (unless the auroras are exceptionally bright) ideally some distance from any city lights, with eyes adjusted to the darkness, and with few clouds and no haze.  The lights are most likely to be  found to the north of your location, but the further north you are, the more likely they are to be overhead.  (Switch north and south if you’re in the Southern Hemisphere.)

Now, something else you may have seen is this map, due to accuweather.com.  The map shows where there likely will be cloud cover (red and yellow) and clear skies (green), but in one respect it is badly misleading: it has a line on it that separates the region where the auroras might be visible from the region where they are “NOT VISIBLE”.  Well, do not entirely lose heart if you are a bit south of that line, and also, don’t be very sure of things if you are north of it.  No one can predict very precisely where that line will be, and it will move around (quite likely northward) as time wears on following the CME’s arrival.

AccuWeather's prediction for viewing conditions tonight.  While their ability to predict the red, yellow and green regions (based on cloud cover) is not in question, no one can reliably predict the green line that determines where the auroras might potentially be seen.
Accuweather’s prediction for viewing conditions tonight. While their ability to predict the red, yellow and green regions (based on cloud cover) is not in question, no one can reliably predict the green line that determines where the auroras might potentially be seen.

By the way, let’s ignore the breathless headline of the accompanying AccuWeather article: “Dazzling Northern Lights Anticipated Tonight” — that’s journalistic license at work.  (Not to mention the article’s scientific misstatement about protons.) The auroras generated by the solar flare may be anything from a dim, quietly beautiful green wash to a bright red and/or multi-color light show, and no one, certainly not AccuWeather, can tell you which it will be, especially not in a specific time or location.  So be prepared for something that’s beautiful and subtle, not dazzling.  If in fact you find yourself dazzled, count yourself very lucky!

Finally: one good way to know whether you should go outside to look at the auroras is to keep an eye on this graph. The bottom of the four plots on the graph is marked “Estimated Kp”, and you can see that it’s showing green bars most of the time. But if the most recent bar is red, that means the earth’s magnetic field is significantly disturbed, and there’s a good chance of auroras further south than usual, in which case you should definitely consider going outside and taking a look. The higher the red bar, the more southerly the auroras are likely to go.  (If someone can remind me where one can find more timely updates of the Kp estimate, I’d appreciate that.)

Meanwhile, the later the CME arrives (and it is already a bit late) the less likely it is that the CME hits the earth head on, and the less likely it becomes that we’ll see auroras far from the poles tonight. UPDATE: The CME has arrived, a little while before sunset in New York. If in fact we do get auroras at all, it’s quite possible you’ll be able to see them an hour or two after sunset in the northern United States and Canada.

Wishing you good luck with one of the first aurora opportunities of 2013! And if you see one, think to yourself: physics is beautiful!

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10 Responses

  1. Mark “Obviously that flare and associated CME were not Earth directed — otherwise, y’all would have remembered it from its disastrous effects”

    and yet more proof of Global Warming some may say. (I had to get that dig in.)

    But some winter nights in Alpena Michigan in the late 1940’s were as spectacular as recent photos from Alaska. If you get a chance do not miss seeing the “big ones”. You will remember them.

  2. Gaia got you with her dazzling light show. Gaia is like a girl who bats her eyes at you so you won’t noticed her weakness or carelessness that she unwittingly showed and therefore need to hide it somehow by batting her eyes at you… a dazzling light show!

    There is something terrifying about auroras, it means that the Earth’s magnetosphere was breached and allowed tons of harmful CME particles to enter our atmosphere. Mars’ magnetosphere was weak and failed to deflect a massive CME that consequently ripped off its atmosphere. Anyways, Gaia advocates say it’s alright, she is just sampling the ‘pathogens’ so she can manufacture appropriate defences… Like a mother that instinctively kiss her dirty baby to sample the pathogens so she can manufacture anti-bodies and incorporate it in her milk… to raise the immunity of her baby. So it’s alright auroras reached new york?

    The sun sneezes from time to time and we called it CME and it annoy the neighborhood. Our magnetosphere is like a handkerchief that we use to cover our noses when somebody sneeze.. never mind the Gaia advocates, I think our handkerchief is inadequate what can we do about it?

    1. NOAA space weather forecast is valuable for satellite operators and earth based communication companies, but it’s only for contingencies.. I wish there is a long term planning going on.

      My GPS is still working, no plan to put the 24-satellite GPS constellation to sleep? Probably the 5-satellite THEMIS constellation will be working in the storm, poor satellites I wish they will be alright.

      1. They didn’t email me, now I lost the count.. 4 from ESA cluster.. joined by 5 Themis then 2 then 2 went to lunar orbit and became Artemis… Aww! I must renew my subscription 😀

  3. This is boring. I want more Michio-Kaku-speak. Did the auroras have anything to do with the creation of the universe?

  4. See what your post did?! 🙂 Now I am digging around…

    Spaceweather.com has the web pages of that memorable event in 2003.


    Based on my review of those pages, the night of the brilliant red auroras in Washington D.C. occurred on the 29th, not the 30th — the CME from that flare was bookin’. It would have been most appropriate had it arrived Halloween night — since it created a blood red sky that evening…..

    That ugly sunspot, 486, which caused all the trouble, unleashed a megaflare a week later, X40+ (revised estimates, IIRC). Obviously that flare and associated CME were not Earth directed — otherwise, y’all would have remembered it from its disastrous effects on our satellites and electrical grid, like an electronic ‘Pearl Harbor’.

  5. Hi Dr. Strassler,

    I’d like to add a bit of info about the possibilities of seeing auroras in the United States, please see http://www.swpc.noaa.gov/info/kp-aurora.html (sorry I don’t know of any similar maps for the eastern or southern hemispheres.)

    From my experience, the last time auroras were seen in the Washington D.C. skies with plenty of light pollution (38 N latitude) was October 30 2003. See:


    It was associated with the flare that occurred on the 28th. Given that this recent flare was not even an X-class event, it makes me wonder if there’s already a bit of hype. This solar max period is turning out to be a big disappointment, having been ‘spoiled’ by the last one which occurred 2002-2004 with so many aurora events. [In a way, we may be dodging a bullet, as we’ve only become more dependent on satellites and the aging electric power grid which are sensitive to the proton and magnetic flux changes these storms bring]

    Sorry for straying off topic a bit.

    Happy watching!

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