While some experts think the threat from the solar storm passed by Thursday afternoon, space weather forecasters said it's still too early to relax. That's because there's a chance the storm's effects could continue and even intensify through Friday morning.
And while this solar storm may have fizzled, others may be lining up in the cosmic shooting gallery in the coming, days month and year, the scientists agree.
"It looks to me like it's over," NASA solar physicist David Hathaway said late Thursday afternoon, after noticing a drop in a key magnetic reading.
That conclusion is premature, said Doug Biesecker, a space scientist at the National Oceanic and Atmospheric Administration's Space Weather Prediction Center in Boulder, Colo., which forecasts solar storms. He pointed to an increase in a different magnetic field measurement.
The storm, which started with a solar flare Tuesday evening, caused a stir Wednesday because forecasts were for a strong storm with the potential to knock electrical grids offline, mess with GPS and harm satellites. It even forced airlines to reroute a few flights on Thursday.
It was never seen as a threat to people, just technology, and teased skywatchers with the prospect of colorful Northern Lights dipping further south.
But when the storm finally arrived around 6 a.m. EST Thursday, after travelling at 2.7 million mph, it was more a magnetic breeze than a gale. The power stayed on. So did GPS and satellites. And the promise of auroras seemed to be more of a mirage.
"I think we just lucked out," Jeffrey Hughes, director of the Center for Integrated Space Weather Modeling at Boston University, said Thursday afternoon. "It just didn't pack as strong a magnetic field as we were anticipating."
Scientists initially figured the storm would be the worst since 2006, but now seems only as bad as ones a few months ago, said Joe Kunches, a scientist at the NOAA centre. The strongest storm in recorded history was probably in 1859, he said.
"It's not a terribly strong event. It's a very interesting event," Kunches said.
Forecasters can predict the speed a solar storm travels and its strength, but the north-south orientation is the wild card. This time it was a northern orientation, which is "pretty benign," Kunches said. Southern would have caused the most damaging technological disruption and biggest auroras.
North American utilities didn't report any problems, said Kimberly Mielcarek, spokeswoman for the North American Electric Reliability Corporation, a consortium of electricity grid operators.
Astronomers say the sun has been relatively quiet for some time. And this storm, forecast to be strong and ending up minor, still may seem fiercer because Earth has been lulled by several years of weak solar activity.
The storm is part of the sun's normal 11-year cycle, which is supposed to reach a peak next year. Storms as large as the latest one will probably happen several more times as the cycle ramps up to that peak, scientists said.
The region of the sun that erupted can still send more blasts our way, Kunches said. Another set of active sunspots is ready to aim at Earth.
"This is a big sun spot group, particularly nasty," NASA's Hathaway said. "Things are really twisted up and mixed up. It keeps flaring."
Storms like this start with sun spots. First, there's an initial solar flare of subatomic particles that resembles a filament coming out of the sun. That part usually reaches Earth only minutes after the initial burst, bringing radio and radiation disturbances. Next is the coronal mass ejection, which looks like a growing bubble and takes a couple days to reach Earth.
Solar storms have three ways they can disrupt technology on Earth: with magnetic, radio and radiation emissions. In 1989, a strong solar storm knocked out the power grid in Quebec, causing 6 million people to lose power.
For North America, the good part of a solar storm — the one that creates more noticeable auroras or Northern Lights — was likely to peak Thursday evening. Auroras were likely to dip only as far south as the northern edges of the United States, Kunches said, but a full moon would make them harder to see.
Solar storms can bring additional radiation around the north and south poles — a risk that sometimes forces airlines to reroute flights. On Thursday, Delta Air Lines and United Airlines sent 11 flights to Asia on a more southern route rather than their more common path over the Arctic. Three American Airlines flights flew lower than normal over the northernmost parts of their routes to Japan and China.
AP Business Writers Josh Freed and David Koenig contributed to this report.
NOAA Space Weather Prediction Center: www.swpc.noaa.gov
NASA on solar flare: http://www.nasa.gov/mission_pages/sunearth/news/News030712-X1.5.html
Follow Seth Borenstein at http://twitter.com/borenbears