Hours after the storm arrived, officials said were no reports of problems with power grids, GPS, satellites or other technologies that are often disrupted by solar storms.
But that still can change as the storm shakes the planet's magnetic field in ways that could disrupt technology but also spread colorful Northern Lights. Early indications show that it is about 10 times stronger than the normal solar wind that hits Earth.
The storm started with a massive solar flare Tuesday evening and grew as it raced outward from the sun, expanding like a giant soap bubble, scientists said. The charged particles were expected to hit at 4 million mph.
The storm struck about 6 a.m. EST in a direction that causes the least amount of problems, said Joe Kunches, a scientist at the National Oceanic and Atmospheric Administration's Space Weather Prediction Center.
"It's not a terribly strong event. It's a very interesting event," he said.
Forecasters can predict the speed a solar storm travels and its strength, but the north-south orientation is the wild card. And this time, Earth got dealt a good card with a northern orientation, which is "pretty benign," Kunches said. If it had been southern, that would have caused the most damaging technological disruption and biggest auroras.
"We're not out of the woods," Kunches said Thursday morning. "It was a good start. If I'm a power grid, I'm really happy so far."
But that storm orientation can and is changing, he said.
"It could flip-flop and we could end up with the strength of the storm still to come," Kunches said from the NOAA forecast center in Boulder, Colo.
North American utilities so far have not reported any problems, said Kimberly Mielcarek, spokeswoman for the North American Electric Reliability Corporation, a consortium of electricity grid operators
A massive cloud of charged particles can disrupt utility grids, airline flights, satellite networks and GPS services, especially in northern areas. But the same blast can also paint colorful auroras farther from the poles than normal.
Astronomers say the sun has been relatively quiet for some time. And this storm, while strong, 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. Solar storms don't harm people, but they do disrupt technology. And during the last peak around 2002, experts learned that GPS was vulnerable to solar outbursts.
Because new technology has flourished since then, scientists could discover that some new systems are also at risk, said Jeffrey Hughes, director of the Center for Integrated Space Weather Modeling at Boston University.
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 solar physicist David Hathaway said. "Things are really twisted up and mixed up. It keeps flaring."
Storms like this start with sun spots, Hathaway said.
Then comes an initial solar flare of subatomic particles that resemble a filament coming out of the sun. That part from this storm hit Earth only minutes after the initial burst, bringing radio and radiation disturbances.
After that comes the coronal mass ejection, which looks like a growing bubble and takes a couple days to reach Earth.
For North America, the good part of a solar storm -- the one that creates more noticeable auroras or Northern Lights -- peaks Thursday evening. Auroras could dip as far south as the Great Lakes states or lower, Kunches said, but a full moon will make them harder to see.
Still, the potential for problems is widespread. Solar storms have three ways they can disrupt technology on Earth: with magnetic, radio and radiation emissions. This is an unusual situation, when all three types of solar storm disruptions are likely to be strong, Kunches said.
In 1989, a strong solar storm knocked out the power grid in Quebec, causing 6 million people to lose power.
Solar storms can bring additional radiation around the north and south poles -- a risk that sometimes forces airlines to reroute flights.
Satellites can be affected, too. NASA spokesman Rob Navias said the space agency wasn't taking any extra precautions to protect astronauts on the International Space Station from added radiation.
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
The Associated Press contributed to this report.