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. "It's hitting us right in the nose," said Joe Kunches, a scientist for the National Oceanic and Atmospheric Administration (NOAA).
He called it the sun's version of "Super Tuesday."
Scientists 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.
"This is a good-size event, but not the extreme type," said Bill Murtagh, program coordinator for the space weather center.
The solar storm is likely to last through Friday morning, but the region that erupted can still send more blasts our way, Kunches said. He said another set of active sunspots is ready to aim at Earth right after this.
The charged particles hit Earth at 4 million mph.
NASA solar physicist Alex Young added, "It could give us a bit of a jolt." But he says this is far from a super solar storm.
The storm is coming after an earlier and weaker solar eruption happened Sunday, Kunches said. The latest blast of particles will probably arrive slightly later than forecasters first thought.
That means for North America the "good" part of a solar storm - the one that creates more noticeable auroras or Northern Lights - will peak Thursday evening. Auroras could dip as far south as Colorado but a full moon will make them harder to see.
Auroras are "probably the treat we get when the sun erupts," Kunches said.
But there is potential for widespread problems. 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.
That means "a whole host of things" could follow, he said.
The magnetic part of the storm has the potential to trip electrical power grids. Kunches said utility companies around the world have been alerted. The timing and speed of the storm determines whether it knocks off power grids, he said.
In 1989, a strong solar storm knocked out the power grid in Quebec, causing 6 million people to lose power.
Solar storms can also make global positioning systems less accurate, which is mostly a problem for precision drilling and other technologies, Kunches said. There also could be GPS outages.
The storm also can cause communication problems and added radiation around the north and south poles, which will probably force airlines to reroute flights. Some already have done so, Kunches said.
Satellites could be affected, too. NASA spokesman Rob Navias said the space agency isn't taking any extra precautions to protect astronauts on the International Space Station from added radiation.
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 peak storminess 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.
A decade ago, this type of solar storm happened a couple of times a year, Hughes said.
"This is a good-size event, but not the extreme type," said Bill Murtagh, program coordinator for the federal government's Space Weather Prediction Center.
(KUSA-TV © 2012 Multimedia Holdings Corporation with The Associated Press)