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December 10, 2020

Northern lights may be visible in Pennsylvania on Thursday night

The viewable range of the aurora borealis will be pushed farther south than usual due to celestial storms

Nature Astronomy
Northern Lights 2020 PA IMAGES/SIPA USA

Aurora borealis forecasts from the University of Alaska-Fairbanks' Geophysical Institute shows a chance of seeing the northern lights in Pennsylvania on Thursday night, Dec. 10. Stargazers will likely have to travel north of Philadelphia to catch a glimpse. The photo above shows the norther lights in the sky above a castle in England.

A combination of atmospheric events may give some Pennsylvania residents the chance to see the colorful northern lights over the next few nights, according NOAA scientists and geomagnetic storm watchers.

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Geomagnetic storms are temporary disturbances of the Earth's magnetosphere. They're caused by a solar wind shock wave or a cloud of magnetic field that interacts with the Earth's magnetic field. When a geomagnetic storm coincides with a solar flare, the visibility of an aurora — usually seen close to Earth's two magnetic poles — can be extended.

The NOAA's Space Weather Prediction Center put a Geomagnetic Storm Watch into effect from Dec. 9 through Dec. 11, with the strongest storm level (G3) forecast for Thursday night, Dec. 10. The storm level drops to G2 on Friday night, reducing the probability that the aurora borealis will be seen this far south. 

The aurora forecast from the University of Alaska Fairbanks shows that stargazers may be able spot auroral activity into Pennsylvania on Thursday night.

The Space Weather Prediction Center has a more conservative estimate of the aurora's visibility, though some activity may still be observed.  

Catching a glimpse of the northern lights won't be an easy feat, but clear skies across much of Pennsylvania and the Northeast U.S. will be a big help.

Remote areas that are distant from light pollution will be the best places to be on the lookout. Locations such as the Poconos are ideal, but some areas in the Delaware Valley may be suitable on Thursday night, as well. Look for the aurora borealis to be visible low on the horizon.

On Dec. 7, a large solar flare coincided with a coronal mass ejection to create the conditions we're seeing this week.

A coronal mass ejection sends a cloud of magnetically charged particles from the solar corona, reaching Earth in about one to three days. Solar flares are plasma bursts of X-rays and energy that travel at the speed of light, reaching Earth in about 8 minutes.

The visibility of the colorful light seen in an aurora is extended on Earth when these two events create a large geomagnetic storm.

"When the electrons and protons from the sun collide with oxygen and nitrogen in the Earth’s atmosphere, they gain energy," UAF scientists explain. "To get back to their normal state, they release that energy in the form of light. The principle is similar to what happens in a neon light. Electricity runs through the light fixture to excite the neon gas inside, and when the neon is excited, it gives off a brilliant light."

The most common color seen during these events is green, but there is a possibility that shades of red, pink or blue will be visible, too.

The videos below provide a deeper explanation of what causes the northern lights and how they appear in their most visible locations in the Arctic Circle.