The Southern Lights - Aurora Australis

Wind Turbine looking North - Mawson

Monday 30th May 2011.

Word went around that there was an active auroral display in progress, it was about 8:30 pm. I had been waiting for an opportunity to photograph an aurora at a reasonable time of night. I often see them out of my bedroom window late in the night and more recently in the early morning when starting work, but I needed a couple of hours to play with various camera settings to get acceptable photographs.

So after quickly dressing up in full kit to keep warm in the -20 degrees C outside I set off. There was a display that was in decline and although disappointed I was able to determine the settings needed on my camera. Just as I was considering packing up the intensity of the aurora increased and over the next hour I was transfixed by an amazing display.

The Ionospheric Prediction Service describes the Aurora a spectacular natural phenomenon occurring in the earth's upper atmosphere, associated with powerful emissions from the sun and geo-magnetic disturbances. They are seen mostly at high or polar latitudes but, occasionally may be seen at middle latitudes when a really large event occurs. For example, during a huge disturbance in March 1989, there were aurorae seen over northern Australia in Exmouth (WA) and in the northern hemisphere, as far south as Texas.

Aurorae are caused by high energy charged particles from the sun, such as electrons, entering the magnetosphere of the earth. This is most likely to happen during a geo-magnetic storm, resulting from the bombardment of the earth by solar particles following a Coronal Mass Ejection (CME).

Once within the magnetosphere, the solar particles interact with the earth's magnetic field, spiralling around the field lines and following them towards the poles…. and are also drawn downward into the ionosphere. In the ionosphere, they strike molecules and atoms of air at around 100 kilometres from the earth's surface (ego, Nitrogen and Oxygen) causing them to radiate light. This light creates the beautiful colours of the aurora!

The chemical composition of the ionosphere varies greatly with altitude and hence so does the colours produced by the incoming solar particles.
Winds blow through the ionosphere where the light emitting atoms are, causing them to shift in waves and ripples. The richly structured Auroral displays exhibit numerous shapes and forms such as bands, arcs, rays and sheets. No two auroral displays are alike and they may vary considerably in shape and brightness over timescales from seconds to minutes. For more technical information about Aurora go to: http://www.spaceacademy.net.au/env/terra/aurora/aurora.htm

Tankhouse looking West - Mawson