Discover where you can see the aurora australis – the southern lights – right here in Australia.
Most people know about the northern lights, but few realise that its southern counterpart, the aurora australis, can be seen from Australia. With longer nights, winter is the perfect time to find it.
IT WAS STEVE LEE who alerted me to it. He is head of the night assistants at the giant Anglo-Australian Telescope in north-western New South Wales. From a vantage point high on the outside walkway of the dome, he has a panoramic view of the horizon. Very few things elude this expert sky-watcher. “I think there’s an aurora developing,” he told me over the phone. “Better get out and have a look.” And that’s exactly what I did, after pulling on a jacket to stave off the chill of the winter’s night. But it was one thing for Steve to see the first hints of an auroral display from his mountain-top viewpoint, and quite another for me, from my home 20km away, on the edge of the small bush township of Coonabarabran.
The problem wasn’t urban light pollution – the dark skies around Siding Spring Observatory are protected by legislation – but geography. Coonabarabran’s location in the north of the state means that any auroral activity is only visible on the far southern horizon. And, inconveniently, my house was on the north-facing slope of a hill. I hopped over the back fence and headed up the hill.
Sure enough, once I reached the top, my eyes then fully adapted to the dark, I could see a faint band of pinkish light extending along a few dozen degrees of my southern horizon. Not the glow of streetlights – the nearest town in that direction is Bathurst, 240km away. No, this was the rarest of celestial phenomena – a display of aurora australis over northern NSW. Captivated, I stood in silence and watched for an hour, until the pink glow faded into darkness.
THAT EVENT WAS a long time ago, when aurora-watching was entirely a matter of luck, and there was no prospect of recording the faint fingers of light without highly specialised equipment. It’s very different today. Aurora photography is within the reach of many point-and-shoot cameras, and websites such as spaceweather.com provide alerts on the state of the Earth’s environment gleaned from a flotilla of spacecraft.
Even so, I would have struggled to make any photographic record of my brief aurora australis encounter. In this game, the mantra is ‘location, location, location’ – and Coonabarabran is just too far from the South Pole to see a spectacular display. Residents of Tasmania, particularly around Hobart and along the south coast, are in a much better position to catch the southern lights.
To understand why, you need to know something of the way aurorae are formed.The action starts in the Sun’s atmosphere. Here intense magnetic fields churn the outer layers into sunspots, occasionally hurling huge quantities of plasma into space as their force-lines stretch and break. These solar flares propel subatomic particles into space at high velocity, and, if the direction is right, they interact with the Earth’s magnetic field a couple of days later.
That interaction is itself a convoluted process that sees the particles whizzing over the Earth’s North and South poles, only to be turned back on themselves in the elongated sheath of magnetism that extends from the planet’s night-side. This focuses them so that they eventually plunge into our atmosphere in two doughnut-shaped rings, centred on each magnetic pole, and each having a radius of 20 to 30 of latitude.
It is in these so-called auroral ovals that accelerated particles excite atmospheric oxygen and nitrogen to glow with a rainbow of characteristic colours. In the most intense geomagnetic storms, when the Earth is heavily bombarded by high-velocity particles, displays become brighter, and the auroral ovals spread to include latitudes nearer the equator.
But how do the colours come about? Surprisingly, they are quite specific in their dependence on particle energy and atmospheric pressure. Green is emitted by excited oxygen atoms at heights of 100–200km. Above about 200km, the more rarefied atmosphere switches oxygen’s green light to red. Below 100km, nitrogen molecules are stimulated in the most intense aurorae to glow with red, blue and violet light. This can paint a magenta tinge on the lower edge of bright aurorae.
Complementing the colours is the fact that the auroral glow is produced in thin vertical sheets, often with the appearance of curtains waving slowly in the breeze of particles coming from the Sun. Green is the predominant colour at these lower levels, but it is frequently surmounted by a red glow broken into slowly varying vertical rays. No wonder the Laplanders call the northern equivalent ‘the dancing lights’.
It’s now possible to see why the red colouration so often dominates images of the aurora australis made in Australia. And why, all those years ago, I could see only a pinkish glow in the southern sky. Even the most southerly parts of our continent lie a long way north of the Antarctic auroral oval. Except in the most intense geomagnetic storms, the oval is well below the horizon of Australian observers, and the lower levels of aurorae are invisible. But the vertical red rays can extend upwards to 600km and more, allowing them to protrude above our southern horizon.
SADLY,THERE’S NO escaping the fact that the most brilliant displays are seen, in a truly awe-inspiring experience, from beneath the auroral oval itself. Occasionally, such a display will climax with a rare trick of perspective, in which the parallel light columns seem to radiate from a point almost overhead.They produce a corona, with vivid colours and a motion reminiscent of finger-like crystals precipitating out of a super-saturated chemical solution.To see this magical phenomenon in the southern hemisphere would require a winter expedition to Antarctica. But it can be experienced in the northern Arctic, with Scandinavia, Alaska and Canada being the most popular destinations.
During the past four years or so, I’ve been privileged to lead wintertime expeditions to Norway, Sweden, Finland and Iceland to view the aurora borealis – the ‘northern dawn’. So far, we’ve been lucky, both with the weather and auroral activity level.That’s not entirely accidental.The occurrence of auroral displays is heavily dependent on the Sun’s level of magnetic activity, which varies cyclically over an 11-year period.The current cycle’s peak occurred around 2014, and activity is now slowly declining. There’s still, however, great potential for aurorae this winter. Aurora hunters can maximise their chances of seeing a display by following the guidelines on the previous page.Take heart, too, from the fact that the most recent display energetic enough to be seen from large areas of mainland Australia was just over a year ago, in June 2015.
At the end of the day, no matter where you are observing from, seeing an aurora still depends on luck. Often, it is completely unexpected, as was the case with my hilltop encounter all those years ago. Even astronauts aboard the International Space Station can’t take it for granted as they fly over the auroral ovals, hoping for that privileged view of the aurora from above.
Most unexpected of all, though, are the truly out-of-this-world aurorae that are occasionally seen on other planets.All four of the Solar System’s gas giants – Jupiter, Saturn, Uranus and Neptune – have strong magnetic fields, and all of them exhibit auroral displays from time to time. More mysterious are those that have recently been detected on Mars by NASA’s orbiting MAVEN spacecraft.They have been seen in ultraviolet light in unexpected regions of the Martian atmosphere, and are especially puzzling given Mars’s low atmospheric pressure and almost complete lack of a magnetic field.
So, if you thought research had unlocked all the mysteries of the aurora, think again.The dancing lights still hold many secrets...
“Reaching high into the sky and vibrantly coloured, this was the most stunning aurora I have ever witnessed. The Moon, Venus and International Space Station also appear as dots in this image.” Calverts Lagoon, Tasmania