[UPDATE May 10, 4:00 pm Boston Time, 10:00 pm EU time: AURORAS MAY BE ACTIVE NOW!]
I don’t use exclamation marks in blog post titles lightly. For those of us hoping to see the northern and southern lights (auroras) outside their usual habitat near the Earth’s poles, this is one of those rare weekends where the odds are in our favor. NOAA’s Space Weather Prediction Center has issued a rare G4 forecast (out of a range from G1 to G5) for a major geomagnetic “storm”.
Though the large and active sunspot from earlier this week has moved on, it has been followed by an even larger group of sunspots, so enormous that you can easily see them with eclipse glasses if you’ve kept your pair from last month.
Powerful solar flares (explosions at the Sun’s visible surface) and the accompanying large coronal mass ejections (“CMEs”, huge clouds of subatomic particles that stream across space from the Sun toward the planets) keep coming, one after another; the second-largest of the week happened just a few hours ago. In the next 24-72 hours, the combined effects of these CMEs may drive the Earth’s magnetic field haywire, leading to northern and southern lights that are much stronger and much more equatorial than usual.
How far south might the northern lights reach? That’s hard to predict, unfortunately. But it wouldn’t be surprising if they reached midway across the United States, and across much of Europe.
If you decide to go looking, keep in mind that dark skies are so important; the auroras can seem quite bright in a dark sky, but they are easily lost to light pollution from city lights or even nearby street lights. Make sure to turn off your car headlights and let your eyes adjust to the dark for a few minutes. The auroras are typically to the north (in the northern hemisphere), but I’ve seen them directly overhead in a strong storm. They’re most often green, but other colors may appear, if you’re lucky. If you’re not sure whether you’re seeing them, take a photo; the camera can pick up dim light and its color more effectively than your eyes can.
As for when to go looking — auroras might happen at any time, from a few hours from now through the weekend, and would potentially be visible whenever the sky is dark. For more detailed information, there are two sources of data that I find useful to monitor:
- First, at this site, you can find near-real-time data on the solar wind— the flow of particles from the Sun — from the ACE satellite, which orbits the Sun almost a million miles from Earth. If you see a sudden wildness in the data, that’s a good sign that a CME has probably passed this satellite, and will arrive at Earth in less than an hour.
- Second, data on the strength of the geomagnetic storm can be found here — but be warned! It is provided only as an average over the past three hours, and only updated every three hours — and so it can be as much as three hours out of date. But if you see the “Kp index” in the red, up around 7 or above, something significant is happening. In a G4 storm, this index can reach 9.
Good luck!!
