With today’s super telescopes, we are better placed than ever to witness the astonishing celestial beauty of stars, nebulae and quasars. But while telescopes are invaluable to our understanding of the distant Universe, there are luminous cosmic energies at play far closer to home that can be seen clearly with the naked eye. Most people have heard tales of the legendary Northern Lights – a.k.a. Aurora Borealis – but their southern cousins, Aurora Australis, make no less magical a spectacle.
Like the work of some immense extraterrestrial artist, auroras are intensely beautiful natural light displays seen in the sky, primarily in polar areas and mostly at night. Forming great swathes of colour, the lights are more visible nearer to the poles due to the longer periods of darkness and magnetic fields.
When observed close to the magnetic pole, aurorae may appear high overhead in what are actually altitudes some 100 km up. Yet from further away, they can also light up the horizon as a vivid green radiance or at times as a hazy red – as if the sun were rising from a bizarre direction.
Aurorae commonly appear either as a diffuse glow or as a curtain-like wash stretching in a roughly east-west direction. Sometimes subtly formed in “quiet arcs”, sometimes constantly shape-shifting as “active aurora”, these wonders of the heavens are dynamic in the way they dance before our eyes.
Woven like a cosmic curtain, each aurora is made up of parallel rays of energised particles aligned to magnetic field lines. See, auroras are produced by charged particles in the outer reaches of Earth’s magnetosphere like electrons and protons clashing with atoms and molecules in the atmosphere.
Image: Samuel Blanc
Auroras are the upshot of something like an astro-pinball machine, with particle collisions electrically exciting atoms and molecules in the upper atmosphere. Most aurorae are green and red, emanating from atomic oxygen, but nitrogen molecules and ions also emit some purple and blue hues.
But what is the ultimate source of these stunning lightshows? It’s our very own Sun. Aurorae are powered by solar winds that constantly steam past the Earth via its upper atmosphere. Solar winds are actually a flow of hot plasma – very thin gas given off by the million-degree heat of the Sun’s surface.
When solar winds hit the Earth’s magnetosphere, they effectively ricochet, and so cough up their energy and material. The newly energised electrons and ions in the geo-space environment around Earth travel along the magnetic field lines to the polar regions of the atmosphere. Cue aurora.
The Southern Lights are observed less frequently than their more familiar northern counterparts – chiefly because so few people live in Antarctica during the austral winter – but such rarity only enhances the extraordinary quality of this atmospheric phenomenon.
Image: Paul Moss
The aurora is named after the Roman goddess of the dawn, Aurora. Borealis comes from Boreas, the Greek name for the “north wind”; Australis on the other hand is the Latin word for “of the south”, since Aurora Australis is only detectable from latitudes in Antarctica, South America or Australasia.
Amundsen-Scott South Pole Station in Antarctica is one of the Earth’s best observation points for taking in the splendour of Aurora Australis. Here the luminescence blankets the sky over the 10-metre South Pole Telescope, which is used to collect data on cosmic microwave radiation and black matter.
Amundsen-Scott is one of three US research posts on the Antarctic run by the National Science Foundation’s US Antarctic Program. Telescopes like the one there represent both our advances into the future and our gaze into the origins of the Universe. Aurorae are as old as the Earth itself, yet there are some stand-out moments in their recent history recorded by man.
In the great geomagnetic storm of 1859, the activity of aurorae was so powerful that they were reported across four continents.
During one night in Boston the aurora was brilliant enough for printed words to be read by their light. Elsewhere, telegraph line operators reported communication minus battery power, but working solely with a current caused by the aurora.
What else is there to say about aurorae, and Aurora Australis in particular? Science will continue to try to explain them, explorers will continue to be stunned by their radiance, and all who see them will need no further convincing that there is no finer painter than nature itself. Perhaps with images so fantastic, we’ve already said too much.
To see more magical images of the aurorae – from space – just follow the link.