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Return of the Northern Lights

What to do to catch an aurora borealis

by Bob Berman
August 12, 2010 11:24 AM | 0 0 comments | 12 12 recommendations | email to a friend | print
A solar Coronal Mass Ejection a week ago sent a shotgun blast of subatomic pellets our way. Ten billion tons of the Sun’s body were hurled in our direction. Our region would have seen a beautiful aurora – if it weren’t overcast.

Now that the ever-so-long sunspot minimum is over and new solar cycle #24 has begun, we can expect future storms. Our region gets wonderful auroral displays – a few a year during the years surrounding solar max. Here are the most important tips for seeing them:

Tip One: If the Moon is a few days on either side of being full, forget it. You need a dark sky. Ditto very hazy, humid skies.

Tip Two: It’s best to be out in the countryside, away from the bright lights of town.

Tip Three: There’s no “best time of night.” Auroras march to a solar clock, not an earthly one. When you read that the Sun has had an explosion, it takes two to four days for the material to arrive here. Experts know this, and inform the media that ‘We might get an aurora tonight.’

We’ve come a long way since sunspot cycle 22 peaked in 1989. On March 13 that year, a dazzling dusk-to-dawn aurora lit up the sky over the entire US and even into Mexico. Huge electrical discharges coursed along the ground beneath the pulsating lights, tripping circuit breakers and causing garage doors throughout North America to open and close on their own. Our entire region had full-sky auroras all night long. Probably 99 percent of auroras are a pale green, but that one had deep, vivid reds as well.

Back then, we did not have today’s never-sleeping sentinels: SOHO, STEREO, ACE, GOES and other spacecraft that watch violent clouds of plasma (broken atom fragments) break loose from the Sun at two million miles per hour. These hurl the energy of one billion hydrogen bombs in our direction. The ACE spacecraft, hovering sunward of Earth, measures the actual shotgun blast of subatomic debris as it sweeps by, to provide an hour or two’s warning of an imminent impact.

Initially flowing past us, some particles snap back and reverberate between Earth’s magnetic poles to create simultaneous auroral displays in the far south and north simultaneously. Photos show that the complex glowing designs at each pole are exact mirror images of each other.

Yet every aurora is just a segment of an enormous, spooky green ring hovering above each pole. Places like Fairbanks, Alaska that sit right below the glowing donut enjoy displays nearly every clear night during solar maxima, like the one that we’re expecting between 2012 and 2014.

Still, it’s not truly rare for mid-northern observers to find themselves right under an expanded auroral oval during times of intense solar activity. On April 6, 2000, an awesome overhead dusk display gave the mid-Hudson Valley pulsating zenith rays and a deep blood-red color. That one was brilliant enough to grab attention at New York’s brightly lit JFK airport. People gaped at what appeared to be blobs of red paint dripping down the western sky and enveloping the crescent Moon. Then, on July 15 of that year, another fabulous aurora lit up the heavens all the way to Georgia and Arizona.

The unpredictability of the patterns is part of their lure. One may see rapid-fire split-second changes, or else the designs may unfold in slow motion as glowing rays, blotches, arcs, lines, curtains or combinations.

Okay, you’ve heard that we “might” get one tonight, and the weather is not too hazy or overcast and the Moon is not near full. Then what?

The problem is that the debris might just miss us. Even if the solar detritus smashes into us, it will only transfer its energy if its own magnetic field is aligned opposite to that of Earth – with south pointing up. We don’t know its magnetic polarity until the swarm of atomic pellets passes the ACE spacecraft, 900,000 miles sunward of us, where its magnetism is measured for the first time.

So to be your own aurora forecaster, you need to access the spacecraft’s data. If you’re even a bit geeky or nerdy, you can handle this. First, get an overall picture of the Sun’s state of quiescence or violence and a three-day forecast here: http://sec.noaa.gov/forecast.html. But you can actually do much better than this. The coolest site for those who are a bit technical, and my very favorite, is the ACE spacecraft real-time data at www.sec.noaa.gov/ace/MAG_SWEPAM_24h.html. Here you’ll read the actual conditions of the incoming solar material!

Three of the five EKG-type graphs are most important. In the topmost graph, look at the white line. This is magnetic polarity. To produce an aurora, it must be near the very top. Next look at the chart of “density.” You want to see at least 50 particles per cc – and remember that this is a logarithmic scale, so in practice you want the graphed line to be between 10 and 100, but closer to 100. Finally, look at speed. You want to see incoming particle speed of at least 700 kilometers per second. (The numbers on the chart change as required by conditions.)

I will offer a few more columns about auroras in our region during the next year. In the end, whatever “prep” you do will be worth it – I promise.

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