I begin my own search for aurora borealis in March in tiny Walhalla, N.D., aka Valley of the Gods, which places me about as close to the action as one can get.
Were I to draw a line around the globe where the aurora borealis is most active, it’d form an oval that is off-center along the north geomagnetic pole. The oval dips south and eastward over North America, reaching farthest south at the continent’s midsection, which is why from North Dakota eastward across northern Minnesota, Wisconsin and upper Michigan is the perfect watching ground in the lower 48.
TIPS FOR PLANNING YOUR TRIP
WHAT TO BRING: Your camera, clothes appropriate for the season and whatever else will make for a relaxing evening under the stars. Binoculars and telescopes are of little value because their scopes are narrow. For the aurora borealis, you want an expansive view.
WHEN TO GO: Plan around the 27-day solar cycle to estimate when the next likely spike in activity will occur. Then allow extra days on both sides of that date. Go to Spaceweather.gov to sign up for free email alerts.
WHERE TO WATCH: The upper Midwest (and the eastern tip of Montana) is the most promising. From elsewhere in the lower 48, your odds improve the farther north you go. Cloudless, dark skies are a must, and face northward on a hill or overlooking a lake or field where no trees will block your view.
Five miles from the Canadian border, Walhalla is situated alongside a winding river gorge surrounded by wooded bluffs frequented by deer, moose, wild turkey, coyote and 80-million-year-old fossils. The Red River Valley, one of the flattest places on Earth, sits to the east. Nearby on the west side is an escarpment that juts 250 feet from the valley floor and offers ideal bleacher seating for watching the aurora.
“It’s nice to be on a hill to see farther north and down on the horizon,” advises Rodney Viereck, director of the Space Weather Prediction Testbed at the National Oceanic and Atmospheric Administration (NOAA), which closely tracks the solar forces responsible for the aurora. Longer sight lines, he says, enable you to see aurorae hundreds of miles to the north. For instance, a Kp=6 aurora overhead in Fargo, N.D., may be visible low on the horizon in Des Moines, Iowa.
More essential than good sight lines, though, is darkness — and North Dakota excels at this. (When the aurore are low on the horizon, as is often the case in the lower 48, city and car lights are a major interference.) Paul Hardersen, a professor of space studies who operates the space-studies observatory at the University of North Dakota in Grand Forks, shows me a satellite image of his state at night. The northwestern corner is lit up like downtown Chicago — “the flares from oil wells burning methane,” he explains. Clusters of light mark the cities — Bismarck, Fargo, Grand Forks — but rapidly fall away. The rest of the state is pitch black.
The best displays are usually between 10 p.m. and 2 a.m., and they peak around midnight. The aurora will brighten and wane several times over the course of one or two evenings, with displays lasting minutes to hours each. A big piece missing in any attempt to view the aurora borealis, however, is a reliable forecast.
Viereck sighs when I ask when I will be able to plan my vacation around an aurora. “We’re missing some of the key physics. We can predict 45 minutes to an hour very well. We can do one day, hmmm, OK. But once we’re at three days [out], we’re pretty much flipping coins.”
Luckily, there is one method for planning in advance: Note the date of the last auroral display and count forward in increments of 27. The sun rotates on its axis every 27 days. If an active area on the surface is pointed toward Earth, it can produce auroras until the active region rotates away. Twenty-seven days later, when the region is facing Earth again, it can energize the aurora again. These active cycles may last three to seven revolutions before quieting.
At Spaceweather.gov, you can find dates for the most recent aurora. You may also register there for free email alerts. You’ll receive a heads-up from NOAA if it detects activity on the sun that is likely to whip the solar winds into a storm. A second alert, with a more precise measurement, will follow in one to two days when the storm is 45 minutes to an hour out and has passed NOAA’s space-weather satellite.