Red storm after midnight is SA delight

By John Yeld Time of article published Apr 19, 2000

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The organisers of the millennium laser show on Table Mountain can eat their hearts out - nature has provided South Africans with the real millennium show by providing a highly unusual glimpse of the southern lights, aurora australis.

Dubbed "red storm after midnight" by astronomers, the celestial spectacle has been witnessed during the past fortnight by scores of puzzled South Africans, who thought it was a very bright meteorite or even burning space hardware.

The "lights", caused by a shock wave of energised particles from the Sun which causes the nitrogen in Earth's lower atmosphere to glow, gave night owls a great show after midnight on the morning of April 7, according to astronomers at the South African Astronomical Observatory near Sutherland.

"It began when Stephen Potter noticed that excess light from the sky was interfering with his attempts to measure faint stars," said his colleague Dave Laney.

"Racing down the steps to see who, as he thought, had left his car headlights on, Potter emerged from the dome to find half the sky covered with the glow of the southern lights.

"Large red patches rose from the south-west, passed slowly across the southern sky, and set in the south-east.

"Occasionally, four to five white/violet rays would cut through the red glow like searchlight beams."

The display continued for three hours, resulting in phone calls from around the country, Dr Laney said.

A controller at Cape Town airport had wanted to know why the sky was red and whether it had anything to do with the close grouping of the crescent moon and three planets seen just after sunset recently, he added.

"But in fact the glowing sky had nothing to do with the planets, and everything to do with the Sun."

On April 4, a powerful, explosive "solar flare" had pushed a mass of charged particles from the Sun's atmosphere toward the Earth at high speed, Dr Laney explained.

Two days later, the shock wave sent energised particles down into the Earth's atmosphere in such numbers and power that northern lights - aurora borealis - were visible across Europe and as far south as Florida in the United States.

Here in South Africa, southern lights covered half the sky at Sutherland and were seen at least as far north as Calvinia.

"Normally the aurora is only visible near the poles, and looks greenish," Laney explained.

"The power to make nitrogen in the lower atmosphere glow bright red isn't usually available. The good news is that the show will "very possibly" be repeated, he added.

"Activity on the Sun is once more nearing maximum, with numerous sunspots, flares and mass ejections, just as it does every 11 years. Over the next year or so, the chance of seeing the South African sky light up will be much higher than normal.

"A powerful geomagnetic storm like the one on April 6-7 can occur on as many as 60 days in the 11-year sunspot cycle."

According to Laney's colleague Case Rijsdijk, an aurora is "very seldom" seen in South Africa.

Usually, only researchers at the Sanae base in Antarctica are lucky enough to see them. "I can't recall the last time this happened - it's not at all common," he said.

Laney pointed out that geomagnetic storms could produce more than just a light show.

For example, the powerful storm of March 1989 caused such powerful current surges through the Canadian electrical power grid that transformers were destroyed and six million people were deprived of power for nine hours.

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