Tasmania's journal of discovery

A special night

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By SHEVILL MATHERS | Our nearest star, the Sun, from a distance of 150,000,000 kilometres, provides us with light and warmth and from time to time a magnificent nighttime ‘laser light’ show. Well, not quite a laser light show, but something on a much grander scale. The Southern Aurora, Southern Lights or Aurora Australis are term used to describe the displays we see in out southern skies when the sun has had a particularly bad day! 

Well, the bad day was perhaps a couple of days before we actually see the results.

The Sun is a giant atomic cauldron of Hydrogen and Helium gases being stirred up by gigantic magnetic fields below the sun’s surface. As we have all seen the results when a pan of milk on the stove overheats, it boils over and the liquid is converted into steam and other products, which we then have to clean up. In much the same way when things get out of control on the Sun, great volumes of highly charged particles are ejected from the surface; these are called Coronal mass Ejections or CME’s for short.

imageThese CME’s are often associated with sunspot activity and can be monitored with special telescopes. If these outbursts are in line with the earth, then there is a good chance that the high speed charged particles will interact with certain particles in our upper atmosphere, particularly near the north and south poles.

At latitude 42 degrees south, southern Tasmania is well placed to receive these charged particles and the result of the solar particles interacting with oxygen, nitrogen and various other atoms along polar magnetic lines, are the green, blue, reds and shades in between that we see as an auroral display.

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Such was the case recently on August 25 when the southern skies were lit up with on of the best displays Tasmanians have seen for many years. The auroral activity extended from due east to due west and covered half the sky up to the zenith. The activity early in the evening from around 7:30 produced a wide range of effects and colours, until later in the evening it settled down to a steady greenish glow as an arc from east to west over Hobart and the Derwent River.

imageBeing a keen scientific and astronomical photographer, I am always set up ready to photograph these events from my own Southern Cross Observatory near Hobart, or from a location which will provide a scenic backdrop to the display. The images reproduced here were taken from my observatory early in the activity and later from the Mt Canopus Observatory site at Cambridge.

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To take these images and retain the fine detail I used a Nikon D100 digital single lens reflex camera fitted with a Nikkor 28 mm lens working at f/2.8, exposures ranged from 3 to 10 seconds.

Shevill Mathers runs the private Southern Cross Observatory Tasmania.
He is Associate Editor of the “New” Sky & Space Magazine, and immediate past President and Editor of the Astronomical Society of Tasmania Inc.

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