May 10 to 12, 2024, saw a world in wonder. The magnitude of the geomagnetic storm that sparked the light show was up there with the biggest – rated extreme or G5 on the global scale. And Tasmania had a box seat.
It’s hard not to be captivated and moved by the show, and the collective awe it inspired. I watched it from my sister’s house south of Hobart, perched on the top of Alum Cliffs, with a clear few south and east. For my parents, who moved from Queensland more than a decade ago, it was their first aurora. For my niece and nephew too.
On the way to the house, I could hear squeals of delight from neighbours out on their patios.
About half an hour into the show, headlights filled my sister’s house and a car pulled into the driveway. Two young Taiwanese visitors, mis-directed by Google maps to the house rather than the Alum Cliff’s lookout, were welcomed inside and onto the veranda from where we watched nature’s spectacular together. They were international TAFE students. One was also an artist.
“We are so lucky,” she said.
It was a sentiment we all shared, along with people posting images on social media from locations around the world – from the far south to the far north from somewhere in between, showing the extended viewing range of the event, which was caused by four large coronal mass ejections the previous week. Think exploding plasma on the surface of the sun.
According to Australia’s Bureau of Meteorology, the last time a G5 geomagnetic storm (storms are rated G1 to G5 depending on severity) was recorded was in 2003. Such storms can also threaten infrastructure and power services. In the US, CBS reported that Elon Musk's Starlink satellites were experiencing a "degraded service”.
Back in Tasmania, we stood mesmerised for more than an hour by the curtains of green, the wash of pink and the bands of light waving through it all. At times, the beams of light reached the zenith of the night sky, reminiscent of Mona’s light show at the Domain.
So, what causes an aurora and what is the best way to see one? I asked Andrew Cole, Professor of Astrophysics at the University of Tasmania.
How would you explain the Aurora Australis to a 10-year-old?
Outer space is filled with electrically charged particles. When they hit Earth’s atmosphere, they can make it light up like a fluorescent light tube. This tends to happen in the polar regions, where Earth’s magnetic field is trapping the charge.
What is really going on when the phenomenon occurs?
There’s a stream of protons and electrons from the sun moving past the Earth at several hundred kilometres per second. When electrons encounter the Earth’s magnetic field, they become trapped, moving along the field lines to the poles. The magnetic field funnels the electrons into the atmosphere in the polar regions and they strike atoms of oxygen or nitrogen molecules.
In the low-density upper atmosphere, the atoms only lose this energy by emitting light, which creates the glow you see. Green and red come from oxygen at different altitudes, and violet comes from nitrogen. There’s light in other colours as well, but the atomic physics and the eye’s sensitivity mean that red, green and violet are the colours we can see.
How can we give ourselves the best chance of seeing the aurora?
The Earth’s geographic and geomagnetic south poles are not in the same place. There’s an offset towards Tasmania that makes us one of the best places to see the Aurora Australis. This is because the geomagnetic poles are not lined up precisely with the spin of the Earth, creating a tilt that means the geomagnetic poles are off-centre.
The best way to see the aurora is to look at the space weather forecast and go somewhere very dark, far from city lights. It’s strongest in a ring around the geomagnetic pole, so you’ll want to be as far south as possible. And you need to be patient. Like any weather phenomenon, forecasting is difficult, and the aurora can come and go without much warning.
Modern cameras are extremely sensitive, so it is unusual that you’ll see a brightly coloured display with the naked eye, even when long-exposure photos are showing the telltale green or red glow.
If the conditions are good (indicated by aurora alerts), try to pick up a faint green tint above the southern horizon with a camera or smart phone. If it is bright enough and the skies are dark enough, try to view it with the naked eye, or film it to capture the movement.
There is a good two-minute explainer by the Bureau of Meteorology, which mentions Tasmania as the place to be.
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So, it seems we were very lucky indeed to see what we did last weekend – a vast light show, visible to the naked eye, at a time of night most Tasmanians were still awake. It felt both ancient and brand new, and will not be forgotten any time soon.
Dr Katherine Johnson is a science writer and novelist based in Tasmania. She has published in The Conversation, Good Weekend (Sydney Morning Herald) and CSIRO’s ECOS magazine. Her fourth novel, Paris Savages, was released in the UK in 2020. More about her and her writing can be seen at KatherineJohnsonauthor.com
