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Long Winter Nights, Dry Air Increase Chance to View Aurora

Igniting across Northern skies, ghostly rivers of light dance overhead each year, emitting vibrant shades of green, blue, pink, red and violet.

While the northern lights, or aurora borealis, are often associated with the onset of another icy winter season, these brilliant, natural light displays can be seen year round and much farther south than the Arctic regions.

Occurring every day in the northern and southern auroral ovals around the poles, the faint glimmer of auroral glow, which is powered by the solar wind, is often shrouded by daylight, and city lights, according to a NASA report.

"Typically the air is drier and less dense in the winter," Meteorologist Randy Adkins said, citing the reason for clearer viewing conditions in much of the northern hemisphere.

Winter also offers longer nights, and a higher frequency of clear skies to view the aurora, which is why they may seem to occur more frequently in the cooler season, but enhanced activity depends entirely on the sun.

"They are not highly predictable," Pennsylvania State University Professor of Astronomy and Astrophysics Lawrence W. Ramsey said, adding that he has seen aurora in Pennsylvania during late-summer.

Auroras are more noticeable and enhanced when the sun fires out clouds of charged particles that collide with and excite more atoms and molecules of Earth's atmospheric gases, primarily oxygen and nitrogen.

As the molecules return to their normal state, they release energy in the form of light.

"Solar activity, flares, (coronal mass ejections) CME's, etc., can greatly enhance the density and velocity of the solar wind causing more collisions and thus more light," Ramsey said.

The color emitted depends on which gas is being excited by the fast-moving electrons and the amount of energy being exchanged, according to NASA.

"Oxygen emits either a greenish-yellow light (the most familiar color of the aurora) or a red light; nitrogen generally gives off a blue light," NASA reports.

The effects of the solar wind are greater near Earth's magnetic poles and weaken farther south from the Arctic or north of the Antarctic.

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"The solar wind particles are charged and thus tend to follow the Earth's magnetic field to the poles and that is why aurora are polar phenomena," Ramsey said.

In the Northern Hemisphere, the results are called the aurora borealis, with the aurora australis being its southern counterpart.