How to see an aurora

Almanac Weekly’s Night Sky columnist Bob Berman in his observatory in Willow (photo by Andrea Barrist Stern)

Almanac Weekly’s Night Sky columnist Bob Berman in his observatory in Willow (photo by Andrea Barrist Stern)

Last week a powerful X-class solar flare erupted smack in the middle of the Sun. It was optimally positioned to affect Earth. We broadcast live solar views the next day on our community observatory, while the mass media correctly warned of an impending aurora. Sure enough, last Friday night we got one.

What’s that, you say? You looked and saw nothing? That’s because last Friday’s aurora only amounted to a bright glow in the northwest. A few low subtle streaks came and went. Later the Moon rose, and its light on high streaky cirrus clouds confused the whole thing. You would have had to be north of Montreal to see an aurora well.

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That’s what auroras do: They can appear as a simple glow. It may be confined to the lower northwestern sky – the favored aurora direction. Or it can materialize as leisurely lines, streaks or arcs that may either be limited to the low northern sky or the whole northern sky or the overhead sky or the entire sky. Or the patterns may change rapidly: They may flicker. They may go from arcs to rays to pulsating blotches. If there’s a color, it’s pale green. But in 2001, our region saw blood-red auroras – which are usually large blotches, and quite rare.

Longtime residents have seen amazing displays around here. There was the all-night, full-sky spectacle on March 13, 1989, and vivid evening displays in the autumns of 2000 and 2001, and a bunch of others too.

So we’re hooked and psyched. How can we make it happen?

If you want near-certainty, join the Alaska tour that I run for the Old Farmer’s Almanac every year. Go to https://specialinteresttours.com and sign up. It’s cheap, its fun and we’ve never yet failed to see great auroras since the early ’90s (knock on wood).

But if you have patience, you’ll eventually see one from your backyard, right here. That’s because we already live outside bright city lights. What we need to happen simultaneously are clear skies two to three days after a major solar eruption that has occurred in the Sun’s center or a bit to the right of center. We also need the Moon to be skinny or absent. We need all of those things to happen.

Oh, and one more thing: After a solar eruption, the angry swarm of plasma heading our way has its own magnetic field, and will only transfer its energy to Earth if it’s aligned opposite to our planet’s magnetism. It’s a 50/50 crapshoot. We won’t know until it sweeps past the Ace spacecraft located a million miles sunward of us. These instruments, called SWEPAM, physically measure the particles. So go to www.swpc.noaa.gov/ace/MAG_SWEPAM_24h.html and check out the real-time graphs.

Here’s how to read it: When the solar material hits the spacecraft, the graph of the particle speed will jump up from a background of about 300 kilometers per second up to something like 800. The particle density graph will also jump up from around 10 to perhaps 100. Equally importantly, the topmost white tracing should be located on the top part of the topmost graph; this indicates the correct polarity for an aurora. A few hours after hitting that spacecraft, it will arrive here.

Another website that I use is the Geophysical Institute, whose aurora predictions are fairly accurate. Go to https://auroraforecast.gi.alaska.edu. Look at their maps. Unfortunately for us, even if they predict a Level 5 aurora – a “high” activity rank, which is what happened last Friday – that won’t be enough to make the aurora oval migrate sufficiently southward to reach us here. We usually experience a Level 5 as a low glow only. So you’re looking for a prediction of a 6 or even a 7. These are quite rare. But if you do see this, you must go out at nightfall and keep watching, if our weather is clear.

We are now one year past what has proven to be a wimpy Solar Max. Nonetheless, auroras often peak in the year after maximum. So don’t give up. It’s not a question of “if,” but “when.”

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