What are The Northern Lights?
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The northern lights, or the aurora borealis, are beautiful dancing waves of light that have captivated people for millennia. But for all its beauty, this spectacular light show is a rather violent event.
Energized particles from the sun slam into Earth's upper atmosphere at speeds of up to 45 million mph (72 million kph), but our planet's magnetic field protects us from the onslaught.
As Earth's magnetic field redirects the particles toward the poles — there are southern lights, too, which you can read about below — the dramatic process transforms into a cinematic atmospheric phenomenon that dazzles and fascinates scientists and skywatchers alike.
Though it was Italian astronomer Galileo Galilei who coined the name "aurora borealis" in 1619 — after the Roman goddess of dawn, Aurora, and the Greek god of the north wind, Boreas — the earliest suspected record of the northern lights is in a 30,000-year-old cave painting in France(opens in new tab).
Since that time, civilizations around the world have marveled at the celestial phenomenon, ascribing all sorts of origin myths to the dancing lights. One North American Inuit legend(opens in new tab) suggests that the northern lights are spirits playing ball with a walrus head, while the Vikings thought the phenomenon was light reflecting off the armor of the Valkyrie, the supernatural maidens who brought warriors into the afterlife.
Early astronomers also mentioned the northern lights in their records. A royal astronomer under Babylon's King Nebuchadnezzar II inscribed his report of the phenomenon on a tablet dated to 567 B.C., for example, while a Chinese report from 193 B.C. also notes the aurora, according to NASA(opens in new tab).
The science behind the northern lights wasn't theorized until the turn of the 20th century. Norwegian scientist Kristian Birkeland proposed that electrons emitted from sunspots produced the atmospheric lights after being guided toward the poles by Earth's magnetic field. The theory would eventually prove correct, but not until long after Birkeland's 1917 death.
At any given moment, the sun is ejecting charged particles from its corona, or upper atmosphere, creating what's called the solar wind. When that wind slams into Earth's ionosphere, or upper atmosphere, the aurora is born. In the Northern Hemisphere, the phenomenon is called the northern lights (aurora borealis), while in the Southern Hemisphere, it's called the southern lights (aurora australis).
"These particles are deflected towards the poles of Earth by our planet's magnetic field and interact with our atmosphere, depositing energy and causing the atmosphere to fluoresce," said astronomer Billy Teets, the director of Dyer Observatory at Vanderbilt University in Nashville, Tennessee.
The bright colors of the northern lights are dictated by the chemical composition of Earth's atmosphere.
"Every type of atom or molecule, whether it's atomic hydrogen or a molecule like carbon dioxide, absorbs and radiates its own unique set of colors, which is analogous to how every human being has a unique set of fingerprints," Teets told Space.com. "Some of the dominant colors seen in aurorae are red, a hue produced by the nitrogen molecules, and green, which is produced by oxygen molecules."
While solar wind is constant, the sun's emissions go through a roughly 11-year cycle of activity. Sometimes there's a lull, but other times, there are vast storms that bombard Earth with extreme amounts of energy. This is when the northern lights are at their brightest and most frequent. The last solar maximum, or period of peak activity, occurred in 2014, according to the U.S. National Oceanic and Atmospheric Administration(opens in new tab) (NOAA), placing the next one in approximately 2025.
Despite plenty of advances in heliophysics and atmospheric science, much about the northern lights remains a mystery. For example, researchers weren't entirely sure how the energized particles in the solar wind get accelerated to their extraordinary speeds (45 million mph) until June 2021, when a study published in the journal Nature Communications(opens in new tab) confirmed that a phenomenon called Alfvén waves gave the particles a boost. Alfvén waves are low-frequency yet powerful undulations that occur in plasma due to electromagnetic forces; the electrons that create the northern lights "surf" along these waves in Earth's atmosphere, accelerating rapidly.