Australia Weather News

Sky-gazers in South Australia's south-east have spotted a mysterious atmospheric phenomenon called Steve.

The arc of purple and white light in the night sky was seen from the south coast to Kingston South East and east to near Bordertown last Friday.

The phenomenon was first named in 2016 after a looming hedge called Steve in the children's movie Over the Hedge, but scientists later gave it the "backronym" Strong Thermal Emission Velocity Enhancement.

Monique McGregor took a photo of Steve above her daughter Fauve in Nene Valley while looking for the Aurora Australis.

"At first, I was confused as to why I was observing an extremely strong beam in the south-west sky," she said.

"Once I realised it was the extremely rare phenomenon Steve, I turned my back on the spectacularly strong aurora geostorm in the southern sky and concentrated on Steve. 

"I couldn't believe I was seeing one of the rarest phenomena to be seen in our sky; hence I wanted to take a photo of my daughter in the foreground to make a lasting memory for her. 

"[It was] a very special moment for us both."

University of Tasmania professor of physics and astronomy Andrew Cole said Steve was caused by the same solar activity that sparked last week's auroras over southern Australia.

However, he said the phenomenon occurred slightly farther north — or farther south in the northern hemisphere — than auroras normally would.

"They really require a very strong aurora to happen, but they don't happen with every strong aurora, so they're a little bit mysterious in some ways," he said.

"People are still researching the underlying physics of what specifically triggers them to occur."

He said auroras occurred when solar activity disturbed Earth's magnetic field and charged particles that then cascaded down through the atmosphere. 

But Steve was more like a welder's arc in that the light was caused by the solar activity heating the upper atmosphere, according to Professor Cole.

"They have the same ultimate kind of cause but slightly different processes into creating the light," he said.

Next appearance hard to predict

Professor Cole said it was hard to predict when or where Steve would be seen again.

All scientists know is that it occurs during strong solar activity.

"That would make the conditions right for seeing an aurora or for seeing Steve, but knowing where to look and when is like predicting where it's going to rain and how hard — you never know until you're in it," Professor Cole said.

Paige Harper saw Steve at Allendale East but did not realise what it was until ABC South East SA posted another photo on its Facebook page.

"[I] was just seeing if there was any colour around my house to head down to the beach for proper photos [of the aurora]," she said.