Wednesday, April 03, 2013

Hoping for auroras, but not tonight

Monaghan Township, York County PA
After a mostly gloomy and overcast winter, the clear skies of this April are very welcome. Yesterday I wrote about how beautiful the morning light is, and last night I enjoyed the nighttime sky every bit as much. With skiing at Roundtop closed for the season and clear skies overhead, the stars are brilliant right now. I keep hoping to see northern lights—Alaska has been treated to some spectacular shows this year—but I’ve yet to see them this year. In fact it’s probably been ten years since I’ve seen a display here, at least in part because of cloudy skies on the few nights when I might have been able to see them.

Northern lights, or aurora borealis if you prefer, are often associated with both the spring and fall equinoxes. That’s because geomagnetic storms, or disturbances in the earth’s magnetic field, are strongest then. In addition to the spring and fall timing, several additional things during these times also signal when might be a good time to look for the lights.

1. Disrupted radio communications, such as with CB radios. These disruptions are often reported on local media, too. If you hear about those, that night and the next night are good times to check.

2. Solar flares, especially significant ones, are also good indicators of northern lights, typically the night after the flare is reported or about 20-30 hours after the flare

Green lights are the most common kind. Once I saw a big red “pom-pom” of northern lights here at the cabin. I clearly remember walking around the mountain in the early evening and having a sense that the air was crackling with electricity. I even saw a red light before the sky was fully dark that day.

Northern lights are seen in the northern sky, of course, here in the northern hemisphere. Usually, the glow from them is subtle this far south, but sometimes they move, which only makes the display more amazing. Cornell University created something called the “K-index” to describe how far south an aurora might travel based on geomagnetic activity. When the K factor gets to a 7, we have a good chance to see auroras in southern PA. You need a K factor of 9 to see auroras in the southern U.S. but a K factor of 2-3 is good enough if you happen to be in Alaska. is the site I use to check on the likelihood of auroras down here. They also have a good explanation of auroras and the k-index, too.

Right now the k-factor is low at a 1, with a 2 predicted for tomorrow. In fact the sun hasn’t produced a flare for nearly two weeks now. I’m hoping that means the next one, whenever it comes, will be strong enough to send auroras down here. But if not, well, the sky is still gorgeous right now and the stars shine like laserbeams in the black night.

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