Solar storms, like the one that began showering the Earth with charged particles overnight, can raise hopes of a rare appearance of the aurora borealis, or Northern Lights, in the Philadelphia area.
But circumstances may not be ideal tonight, for several reasons, including a full moon and possible rainclouds.
This cosmic event also has proved weaker than originally anticipated, and although it could intensify, it may wind up having only minor impact, a federal space weather scientist said this morning during a media conference call.
Instead of reportedly being the most disruptive such event in six years, it might merely be the strongest in six weeks, said Joseph Kunches of the National Oceanic and Atmospheric Administration.
"I wouldn't imagine there are any significant GPS impacts currently," Kunches said this morning. ". . . It's not a terribly strong event."
Powerful solar storms, the result of massive flares on the sun or ejections of material from our star's corona, have the potential to disrupt radio signals, cause power grid fluctuations, interfere with satellites and trigger false alarms in electronic devices.
On the positive side, though, they can also produce spectacular displays of ribbons of colored lights in the nighttime sky as solar radiation interacts with the Earth's magnetic field.
Sightings have happened here. In late October, when even Southern states reported impressive displays, astrophotographer Jeff Berkes of West Chester described what he saw to Space.com: "The auroras only last a few minutes. But hey it was awesome! Haven't seen them here since September 2001." (See his photo: http://bit.ly/wS5s8L.)
The possibility of an encore was suggested by an alert Wednesday from the federal Space Weather Prediction Center: "Aurora may be seen as low as Pennsylvania to Iowa to Oregon."
But overnight, the forecast began calling for a more mild event, which would mean auroras might only get as far south as Michigan and Maine.
Luckily, the "coronal mass ejection" turned out to have a less disruptive electromagnetic orientation, Kunches said.
If the event does intensify, local observers would be wise to check the skies early after dark, because showers could be moving in by 9 p.m., according to weather.com and the National Weather Service.
Another problem will be tonight's full moon, whose light could drown out faint auroras.
Similarly, the farther an observer is from cities and other sources of light pollution, the better the viewing should be.
On the bright side, more opportunities are possible. Not only is the sunspot that produced the latest X-class flares still active on the near side of the sun, but the 11-year sunspot cycle isn't due to peak until next year.
"This is the season now where we can expect more of these types of events," Kunches said.
Another Pennsylvania testimonial from October: "I was surprised to find the auroras out so brightly," Samuel Hartman of State College, Pa., told Space.com. "It was originally supposed to be cloudy all night, but the clouds cleared and the aurora was glowing bright. It made for an excellent show."