The most powerful eruption on the sun in years is extending the range in which the northern lights will be visible to possibly as far south as Pennsylvania – maybe even into the Philadelphia region – and the best chance to see the colorful auroras is predicted to be Saturday night.
The explosion, known as a coronal mass ejection, occurred Thursday. Scientists say it is strongest CME recorded since 2017, and it flung clouds of magnetized plasma into the solar system, creating a geomagnetic storm headed towards Earth.
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The charged particles emitted from the sun interact with the Earth's magnetic field, creating the array for colors in the night sky known as the northern lights or aurora borealis. In normal conditions the northern lights are only visible within the range of about 1,500 miles from the North Pole. Because of the power of this CME the aurora will be more intense, pushing the viewable range of the lights much further south.
But predicting when and where the northern lights will appear is difficult, even for experts.
"The challenge is actually understanding how severe the eruption is on the sun," Derrick Pitts, chief astronomer at the Franklin Institute, said, "and how far down it will reach from the poles of the planet, down towards the mid-latitudes."
Thursday's eruption was the second CME this week. Both were accompanied by solar flares that emitted intense bursts of electromagnetic radiation traveling at the speed of light that reached the Earth about 8 minutes after each occured.
The magnetized plasma from the CME travels slower and can take 15 hours to several days to reach the Earth's magnetic field, which results in the delay between Thursday's eruption and the peak of the expected celestial event. It also makes it difficult to predict precisely when the northern lights will become more intense.
The National Oceanic and Atmospheric Administration's Space Weather Prediction Center maintains an aurora dashboard on its website. It has maps that show nightly predictions of the range of the aurora, other maps that forecast where the aurora will be visible in the next few minutes and more information.
There had been a chance the northern lights would be visible in the region on Friday night but cloudy skies interfered.
On Saturday night, the geomagnetic energy will be stronger and the National Weather Service predicts the sky over Philadelphia will be mostly clear.
The best opportunity to see the northern lights will be as far away from light pollution as possible. Pitts suggested going at least 60 miles north of Philadelphia to get away from the city's lights – the closer to the Pennsylvania-New York border, the better.
Shawn Dahl, coordinator of NOAA's Space Weather Prediction Center, said it's a good idea to stake out the night sky around midnight.
"Usually we're talking about a four-hour window – two hours before midnight, two hours after midnight – but that window of time can broaden the stronger the activity," Dahl said. "The less strong the activity, that window can shorten up, but still a good time to start looking is a couple hours after dark, especially if conditions are favorable."
Look low on the horizon for the aurora, Dahl said. If you can't see anything, try taking a picture with a smartphone and other digital camera, both sometimes can pick up the lights better than the naked eye.
Autumn and spring are the best seasons for the aurora borealis because of the greater tendency for geomagnetic storms. This year, it also is a particularly active time because of the sun's solar cycle: Every 11 years the sun's magnetic poles flip and ahead of this happening there are more frequent CMEs, solar flares and sunspots.
The solar cycle will peak between the end of this year and early 2026. This period is called a solar maximum, Dahl said, which means the sun gets a little more "stressed out" and releases more energy.
So there could be more opportunities to see the northern lights during the next 18 months, but it's impossible to say for sure. Pitts noted that not only do do the eruptions have to occur, they also have to be directed towards Earth so the geomagnetic storm collides with the Earth's magnetic field.
Managing Editor Jon Tuleya contributed to this article.