Dis­cover where you can see the au­rora aus­tralis – the south­ern lights – right here in Aus­tralia.

Australian Geographic - - Con­tents - STORY BY FRED WAT­SON

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...

JAMES STONE

“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

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