AstroBob and the Aurora Borealis

Amateur astronomer Bob Fisher (better known as AstroBob around these parts–much to his chagrin) has been a passionate star-gazer since childhood when he first saw the superbly dark skies of the Adirondacks on camping trips.  A part-time resident of Olmstedville since 1991, he taught earth science and astronomy in New York City public high schools for more than two decades before making his permanent home here in 2006.  Now a substitute teacher in Warren and Essex county schools, he is also an active astrophotographer. He frequently leads astronomy workshops in local schools and libraries, and occasionally serves as a docent at the American Museum of Natural History in New York City.

THE AURORA BOREALIS

On a clear, spring night near Fairbanks, Alaska in the late sixties, I witnessed a sky event of spectacular proportions. Low on the northern horizon, a dimly glowing band of green light appeared. After a few minutes, the band widened, grew brighter with small areas randomly brightening and dimming. As the green band spread to the east and west, long thin parallel rays projected above the band with faint red and purple, pulsing and shimmering. The rays connected and a multicolored dance of wavy curtains formed constantly changing shape and brightness. Eventually, the whole sky was aflame with brilliant colors and for a jaw-dropping finale, the corona: a rapidly rotating multicolored oval where brilliant colors swirled, brightened, dimmed and chaotically blended with the brilliance of the Full Moon. Within two hours, the light faded and vanished just as mysteriously as the performance began. I can assure you that my companions and I had not taken any mind altering substances that night! We had witnessed the best of a common sky event near the Arctic Circle. Aurora Borealis.

Aurora in Fairbanks, Alaska. Picture from http://auroracabin.com/

The Aurora Borealis, commonly known as the Northern Lights, can certainly be one of the most dramatically beautiful of all nighttime sky events. There is a lot of folklore surrounding this phenomenon, so let me give you a brief summary of the latest science to accurately clarify what we know so far.

For the past 100+ years astronomers have observed that the sun undergoes predictable 11 year cycles of electromagnetic activity. Presently, we are nearing the peak of Cycle 24, which will reach maximum activity in mid to late 2013. Sunspots are the key feature in monitoring solar activity. The minimum of the present cycle was reached in 2006. For years the sun had few spots and a few months went by with no spots at all. As of late, the sun may have 100 or more spots on any given day.

Think of a sunspot as a powerful magnetic field. They appear dark against the surface because they block upwelling convective currents where matter slows down and cools. At times, a large sunspot group is capable of releasing an enormous amount of matter and energy into space. If the Earth is in the path of the ejected material, a powerful geomagnetic storm can occur in the Earth’s upper atmosphere right down to the ground triggering powerful and potentially harmful magnetoelectric effects. To get a sense of the how a particular solar storm occurs, I’d like to tell an imaginary story set in the near future. Although this tale is hypothetical, I have based it on real events from the past.

In early November, 2012, an enormous sunspot complex appeared on the west limb of the sun. Two large central spots were surrounded by a few dozen smaller spots of various sizes. At 35,000 miles across, when viewed through a filter, it was easily seen from Earth with the naked eye. Being a manifestation of cycle 24, the complex was about 25 degrees north of the sun’s equator. After a few days as the sunspot group moved to the center of the solar disc, the magnetic field between the two large spots snapped open releasing a massive blob of ionized plasma gas and energy causing a brilliant white light to appear at the site of eruption. This occurrence was observed by dedicated solar observers using an array of ground based and sun orbiting space telescopes. As this supercharged piece of the Sun was propelled into space, Spaceweather.com posted a CME alert  (Coronal Mass Ejection) on its website. They predicted that a massive x-class class solar flare was in progress and that this blob of ionized gas weighing billions of tons would reach Earth’s magnetosphere within 36 to 48 hours. On November 10th, it slammed into the Earth’s magnetic field, reacted with matter in the ionosphere and produced spectacular, multicolored auroras from Canada to Florida. On the downside, several communications satellites were fried and many power grids in the northern hemisphere experienced blackouts.

Although it is impossible to predict the exact date when a powerful solar storm will occur, as we approach the maximum of Solar Cycle 24, the probability for an event of this magnitude is very high.

In early November 1991, during the maximum of Cycle 22, a spectacular show of Northern Lights occurred one clear night over my cabin in Olmstedville, NY.

Here are some photos I took of that event:

Aurora seen from Olmsteadville, 1991 (taken by Bob Fisher)

If you’re interested in seeing this phenomenon for yourself, Spaceweather.com is a reliable site for making aurora predictions. Look to the Sun and stay posted!

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