BIG SOLAR STORM HITTING EARTH

(CNN) -- Youvathana Sok looked up and saw more than just stars in the crisp, clear Maine night sky.

A colorful, spectacular showing of the aurora borealis greeted Sok, a CNN iReporter, and others at Cadillac Mountain in Acadia National park on Friday.

Greens and whites lit up the night sky, treating viewers to a once-in-a-lifetime showing.

Thanks to a relatively strong solar storm, those living in northern parts of the United States had a chance to take in the vivid colors that normally can only be seen from extremely high or low altitudes.

Experts say the combined energy from two recent solar events has arrived, prompting the Space Weather Prediction Center to issue a strong geomagnetic storm watch for Saturday.

Wait. What's a solar storm? Basically, the sun is a giant ball of gas: 92.1% hydrogen and 7.8% helium. Every now and then, it spits out a giant burst of gas that contains magnetic properties called a coronal mass ejection.

Space weather: Fine, with a chance of solar flares

 These ejections are sometimes associated with solar flares, the most explosive events in the solar system. The sun has released two ejections in the past few days, and both are linked to solar flares. NASA says the second flare is an X1.6 class, putting it in the most intense category.

 The energy from those two ejections is now hitting Earth. Space weather experts aren't sure what this solar storm will do.

Earth's atmosphere usually protects us humans, but you might want to keep a flashlight handy. Solar storms can knock out power, interfere with GPS and radio communications -- including those on commercial airliners -- and damage satellites.

 "People on the ground really don't have to worry," said Lika Guhathakurta, a program scientist with NASA's Solar Dynamics Observatory. She said solar storms don't affect humans on the ground, although astronauts could be at risk.

And our technology.

 But don't worry too much. NASA can take steps to protect the crew members on the International Space Station, and satellite operators can turn off sensitive sensors on satellites.

Should we be worried the solar storm will fry our smartphones or other gadgets? "No, very unlikely," Dr. Petrus Martens, an expert on solar flares and a professor in the Department of Physics and Astronomy at Georgia State University, told CNN. "Of course if we lose the (power) grid, that will eventually affect cell phones and the Internet as well."

 Besides power grids and satellites, Martens says other possible impacts are:

• Distortions in GPS readings of up to a few yards. That is not much, but it can be crucial for military applications; for example, targeting by drones.

• Increased corrosion of long pipelines like the Alaska oil pipeline.

• Homing pigeons going off course. (Martens is not joking about that one.)

Solar storms have caused havoc on Earth before. On March 13, 1989,     NASA says some satellites tumbled out of control for hours during what's known as the Quebec Blackout. The space shuttle Discovery was in orbit at the time and had a mysterious sensor problem that went away after the storm, NASA says.

 On the upside, solar storms also create beautiful aurora. Aurora watchers in the northern United States who are outside major metropolitan areas should be watching the skies the next few nights.

"A fantastic display of Northern Lights as far south as the northern half of the U.S." is possible, Martens said.