A large sunspot, dubbed number 930, ejected a major X-3 category solar flare late Tuesday, blanketing two astronauts at the end of a spacewalk with X-rays.

A few hours later, a wave of accelerated protons hit the space station and the attached space shuttle Discovery, but the astronauts had taken shelter behind protective bulkheads and airlocks before it arrived.

The solar storm was expected to produce vivid displays of the aurora borealis, or northern lights, as far south as parts of Europe and the northern United States on Thursday night.

Solar experts also warned the charged particles could threaten high frequency radio communications. Passengers flying in jet aircraft high above the Arctic and Antarctic could also be put at a higher risk for radiation exposure, forecasters said.

Power-grid operators were warned to make sure their systems did not overload from induced current, and satellites in near-Earth orbits were having their positions constantly monitored as the atmosphere expanded from the additional heat and frictional drag caused by the coronal mass ejection.

Image :U.S. Navy Office of Naval Research