Aurora australis one of the best in years

The aurora australis witnessed on Tuesday night was one of the best seen in Australia since the mid-2000s, a Bureau of Meteorology scientist says.

The colourful light show seen above parts of Australia and New Zealand on Tuesday night was one of the best aurora displays in years, an expert says.

The curtains and swirls of red, pink and green light, known as aurora australis, were triggered by a powerful solar flare on mid-Sunday afternoon.

While it wasn't the "biggest" event recorded, the Bureau of Meteorology's Matthew Francis said it was one of the best in the sun's current 11-year cycle of activity.

"We've probably had a dozen or so over the last few years that have been quite good shows for the Tasmanian aurora watchers, but this is definitely one of the best," a research and development scientist in the BoM's space weather services told AAP.

Mr Francis said part of the sun's outer later, the corona, was blown off during Sunday's explosion, producing an immense magnetised cloud.

It took two days for the high-energy particles emitted from the solar flare to reach earth, travelling at a speed of around 700km per second.

In a similar way to field lines on a magnet, energy from these particles were then deposited at the earth's north and south poles.

The florescent-type light we see is produced when the particles strike gas molecules in the upper atmosphere, at an altitude of 150-200km.

While flares are frequent on the sun, explosions as big are fewer.

"And then less often are these explosions directed towards the earth, so there's a few things that have to line up for us to get one of these events," he said.

"In this case, it was quite a strong event, so a lot of energy was deposited and further out from the poles.

"The further away that it's visible from the pole is indicative of a bigger and stronger event."

So why do those in the northern hemisphere see more green light, and those in the south more red?

"The red happens at a higher altitude - and if it's higher up, you can see it from further away," he said.

"But if you're closer to it, you can see the green that happens at a lower altitude. And that tends to be a more a spectacular show."

Countries such as Finland and Norway, for example, are closer to the magnetic north pole than Tasmania is to the south pole.

Mr Francis said it was hard to predict whether the aurora would still be visible from Australia on Wednesday night, but didn't like the chances.

"These events don't typically last days and days and days, so I would suggest ... you've probably missed it."

Source AAP

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