A powerful eruption on the sun's surface yesterday has sent a storm of solar particles and magnetic energy hurtling toward Earth at more than a million miles per hour.
Scientists aren't sure yet what to expect when it arrives late tomorrow or early Friday.
But electric utilities and satellite operators have been advised to prepare for possible disruptions from what is being described as the first big event of the current 11-year solar cycle.
"It's rare. It's unusual. And we do anticipate a strong geomagnetic storm on June 8 and 9," said Ernie Hildner, director of the federal government's Space Environmental Center in Boulder, Colo.
The approaching solar storm is no direct threat to people. And if it arrives at night, it might even produce a rare display of northern lights across the continental United States - possibly as far south as Baltimore, Hildner said.
Solar scientists have been anticipating such solar storms for more than a year. The sun is nearing its "solar maximum," the peak of its sunspot cycle. The failure of a major eruption to occur before now has disappointed many in the solar research community.
"I've been going out there for some time now warning about this solar maximum," Hildner said. "So far it's been a dud, and proven me a false prophet until now. "
The current storm began with a powerful X-ray flare that erupted late yesterday morning from a large region of sunspots now rotating across the surface of the sun.
That was followed by what scientists call a coronal mass ejection - a huge blast of ionized gas and magnetic energy from the same region. The blast was aimed almost directly at Earth.
Hildner said the event hurled about a billion tons of material out from the sun's atmosphere at speeds estimated between 1 million and 2 million mph.
Depending on its exact speed, the first of this cloud of solar debris should arrive in Earth's vicinity by late tomorrow or early Friday.
Sentry satellites orbiting a million miles sunward of Earth will feel its first effects and radio the data to Earth, Hildner said.
That will give scientists and utility managers their first reliable look at the strength and magnetic characteristics of the storm and about an hour's time to prepare for its effects.
"It may get interesting here in a few days," said John Kappenman of Metatech Corp. His company provides electric utilities, pipeline companies and satellite operators with advance warning of solar events that could threaten their operations.
Solar events like this one can induce fluctuations in Earth's magnetic field, triggering potentially damaging voltage surges in long-distance electric transmission lines and oil pipelines and damage to orbiting satellites.
Kappenman said yesterday's solar flare was 20 to 30 times more powerful than one in April.
"We did see a lot of interesting power system problems from the storm in early April," he said. "Bigger storms cause more interesting problems."
A big solar eruption during the last solar maximum, in 1989, triggered widespread power outages in Quebec, and lesser storms since then have caused several major satellite failures.
Such storms also expand Earth's atmosphere, increasing drag on satellites in low orbits and hastening their fall from the sky.
For more information, try www.spaceweather.com.