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Auroras: What are they and how do you spot one in Australia?

A purple and green aurora seen from Mount Nelson, Tasmania
A green and purple aurora seen from Mount Nelson, Tasmania in April(Supplied: Arwen Dyer)

Auroras light up the night sky in ethereal, brilliant colours.

Some people go on a pilgrimage to the very north of the globe — places like Norway and Iceland — to spot the lights.

But did you know it is possible to see an aurora from some parts of Australia too?

Late last month, a moderate geomagnetic storm created a spectacular aurora lit up the skies above Tasmania.

Another weaker geomagnetic storm occurred later than predicted around the north and south poles on November 9. This time, while people living in Alaska saw beautiful auroras in the night sky, we didn't see anything in Tasmania as the storm, which hit in the late afternoon our time, didn't extend far enough north.

While it's difficult to predict exactly when one will occur, there are a few signs to look out for if you're a keen aurora chaser.

How are auroras created?

A halo of green light above the Earth
The Aurora Australis, captured by NASA's IMAGE satellite and overlaid onto a photograph of the Earth.(NASA: public domain)

Principal space and radio scientist in Space Weather Services at the Bureau of Meteorology, Dr David Neudegg, said the beginnings of an aurora come from the centre of our solar system when the Sun spews out plasma filled with electrons and protons into space in what is called a coronal mass ejection (CME).

The plasma ejected in a CME travels 150 million kilometres before slamming into Earth's magnetic field at more than six million kilometres per hour, causing a geomagnetic storm.

Along with potentially causing disruption to power grids and satellites and throwing migratory animals off their game, the storm also produces an aurora.

The aurora is created by the excitation of atoms in the upper atmosphere as the plasma ejected from the Sun travels along our planet's magnetic field lines towards the north and south pole, said Dr Neudegg.

"As the atoms settle back down, the electrons that have been pushed up to high energy, they settle back down to their normal level and give off light," he said.

Because the shockwaves sent out by the Sun are so large, they easily cover the Earth's entire magnetic field, meaning an aurora appears at both poles at the same time. At the south pole, it's called Aurora Australis, while in the north the phenomenon is termed Aurora Borealis.

Just how big the impacts are on power grids and telecommunications, and how far away from the poles the aurora extends depends upon the strength of the storm, which are classified on a scale of one to five.

At the lowest end of the scale, a 'G1' or minor storm may slightly impact the operation of satellites and an aurora can be visible at high latitudes, while a 'G5' or extreme storm can cause blackouts, interfere with radio broadcasts, disrupt GPS navigation and produce auroras that extend much further north and south of the poles.

How often do they occur?

The level of the Sun's activity moves in 11-year cycles, during which there are periods of higher and lower solar activity. The height of activity's called solar maximum, while the quietest point is solar minimum.

Auroras are more frequent in periods of high solar activity around solar maximum when coronal mass ejections are more common.

"Where we are now is on the downslope from the 24th 11-year cycle since we've been keeping records. We're probably a year or so from entering a long and deep solar minimum," Dr Neudegg said.

Moving into a quieter period of space weather means there will be less auroras, though in the right conditions they can still appear.

What do the colours mean?

Green and purple lights in the sky above a lake
An aurora captured from Howden, south of Hobart.(Supplied: Andrew Fuller)

The most common colour seen in an aurora is green, which is produced by molecular oxygen at lower altitudes down to about 100 kilometres. Brownish-red hues are created by single oxygen atoms which are the most common atoms in the atmosphere above 300 kilometres.




Where can you see an aurora in Australia?

The Aurora Australis (Southern Lights) covers the sky.
The Aurora Australis (Southern Lights) covers the sky over Tasmania.(Audience submitted: Leonard Low)

The short story is — the further south, the better.

According to the Bureau's Space Weather Services, a weak G1 storm usually produces an aurora that is visible from Tasmania.

"The best place in Australia is Tasmania. If it's moderately disturbed you'll see fairly reasonable aurora there if you get away from lights and look south," Dr Neudegg said.

But if the weather in space is particularly fierce, the "auroral oval" — or the roughly circular area where an aurora occurs — expands northwards. Storms that are rated as 'G2' may produce auroras that can be seen from the southern coastline of Victoria.

"So people can see aurora in southern Victoria. I know people here in Adelaide who fish — they say they've seen them offshore if they're away from the lights. Probably southern Western Australia as well."

The most extreme grade, a G5, can produce auroras as far north as Queensland.

Even when a storm is happening there are other factors that will determine if you see a good show.

"Whether you can see them is a function of whether it's winter or summer, how much night time you have, and the weather — if it's always cloudy it's much harder to see them. It's a combination of those things," Dr Neudegg said.

Winter is the ideal season for aurora-spotting because it's darker for longer. Even though Tasmania is further south than the mainland, it can be harder to see an aurora in summer because it doesn't get dark until 10 or 11 o'clock at night.

Aurora Australis, seen from the International Space Station in 2012
Aurora Australis, seen from the International Space Station.(NASA: public domain)

And if you can't see the aurora, don't despair. Advances in digital camera technologies may pick up colours you can't see with your eyes.

The human eye comes equipped with cones, that primarily work in the daytime and distinguish colour, and rods that work at night and distinguish light. Rods can pick up very faint light, but you'll only be able to see it in shades of grey and white.

That means to the eye, an aurora will appear mostly as white light, with some very faint colour. But through a camera's sensors, which are better at picking up colour in low light, the aurora may appear to be a vibrant green, red, or purple.

"What to the eye may look a pale green or even a white colour — when you see a digital photograph the colours can be fantastic, it's pulled out all sorts of colours that we can't see with our eyes," Dr Neudegg said.

How do I take a good photograph of an aurora?


Astrophotographer David Finlay said no-one believed him when he said he could take photographs of auroras from Kiama in New South Wales.

He said anyone could photograph an aurora, provided they had the right equipment and camera settings.

"A lot of people ask if they can use their smartphones to photograph them and the basic answer to that is, 'no, not really,'" he said.

It's only in the most intense of space weather that an aurora is strong enough to be captured on a mobile.

"A couple of weeks ago there was an incredibly strong solar storm down in Tassie and some people were able to capture an aurora on their smartphones," he said.

"But you definitely won't be able to do that from Victoria or New South Wales. It's only the most extreme situations, in far southern Tasmania and it's a massive storm, that you'd be able to do it."

What you do need is a digital SLR and a tripod. To capture the intense lights of an aurora, photographers take a long exposure photograph that allows more light to be collected by the camera.

"Start at a 30 second exposure with a wide open aperture. Having the lowest number of the aperture for a lens will open the lens wide open and it will absorb more light," Mr Finlay said.

"And start with an ISO of 3200. If those images are too bright ... work your way down, go down to a 20 second exposure or a 1600 ISO.

It's also best to find an area away from the light pollution of a city or town.

How can I find out when an aurora is going to happen?

You can sign up for email alerts if Space Weather Services is predicting an aurora will be on display in Australia, and they also provide an "auroral oval" tool that shows where the aurora could be visible from on a map.

Mr Finlay uses an app called Solar Monitor to track down Aurora Australis.

The app tells you how fast and dense the solar wind is, and pushes notifications to your phone if the Sun is particularly active.

"Solar Monitor is connected to both satellites and spacecraft. And those satellites monitor space weather conditions, solar wind speed, solar wind density, and you can use that real-time data to estimate if Aurora Australis is going to be visible in Australia," Mr Finlay said.

Red and green coloured lights - an aurora -  in the night sky
It's also possible to see an aurora from New Zealand - like this one, captured from Lake Ellesmere on NZ's South Island(Ben/