The Valkyrior [Valkyries] are warlike virgins, mounted upon horses and armed with helmets and spears. /…/ When they ride forth on their errand, their armour sheds a strange flickering light, which flashes up over the northern skies, making what Men call the “aurora borealis”, or “Northern Lights”.
— Thomas Bulfinch, Mythology
Sorry, Disney fans, we do not today discuss Sleeping Beauty, but the ineffable, lustrous dance of the cosmos. Dazzling humankind for millennia, an aurora is a natural light show in Earth’s sky.
The phenomenon is known by many names. In the northern hemisphere, it is called aurora borealis or the northern lights. Coined by Galileo in 1619, aurora borealis slams together the Roman goddess of the dawn, Aurora, and the Greek word for the north wind, Borealis. Of course, since our planet is an orb, auroras (aurorae) do not only occur in the north. In the southern hemisphere, the lights come from the south, so they are called aurora australis or southern lights. Australis is Latin for southern. Sometimes a broader term, polar lights, is employed, as an aurora is an episode that stems from the poles.
Whatever it’s called, if you have seen an aurora, you are a fortunate human being.
In addition to the visible light and heat that power our existence, the sun produces a harsh jet of charged particles, called the solar wind. Our planet’s magnetosphere protects us on the surface from most of the really dangerous radiation from our star. When the solar wind hits the upper part of our atmosphere – the ionosphere – the magnetic field of the Earth directs the charged particles toward the pole. When ions interact with the atmosphere, mainly nitrogen and oxygen, energy transfers from the solar wind to the atoms in the air. The energy deposition causes the atmosphere to fluoresce, resulting in an aurora!
Most instances of auroras feature the color green, as that is the color oxygen produces at low altitudes when it is excited. At higher altitudes, oxygen generates red wavelengths. The second-most-common hue for an aurora is blue, which arrives thanks to excited Nitrogen atoms. Sometimes, these colors mix and the show might display pink, orange, or yellow.
The form of the light is perhaps more fascinating than the colors themselves. An aurora can appear in various ways: sometimes merely a glow, sometimes a curtain, other times arcs, rays, or spirals. In some instances, the aurora forms a corona, which is a radiating stream of color from one point in the sky.
Because of the nature of the magnetosphere and the solar wind, an aurora radiates from a pole and is, therefore, much more likely to be viewed at high latitudes. The “aurora zone” is the region close to the poles where most of the storms happen; however, sometimes the wind sent by the sun is particularly strong and people closer to the equators can see the aurora. Each occurrence sports a unique “auroral oval,” which is the term for the spots on the planet that can see the lights.
For nearly all of recorded human history, we have marveled at these lights. Cave paintings that date to 30,000 years ago depict auroras; ancient Greek explorers and philosophers noted them; Nebuchadnezzar’s astronomers etched stones about the storms; mythologies worldwide, from Australian aborigines to Native Americans to Vikings, speculated on the meanings and origins of the auroras. Benjamin Franklin postulated on the causes of the lights in 1778. During the American Civil War, soldiers spotted an aurora during the Battle of Fredericksburg in Virginia, an extraordinarily southern display of the northern lights.
We gazed in awe at the lights for thousands of years, but not until 1896 did a Norwegian scientist named Kristian Birkeland arrive at the explanation which would explain the phenomenon.
Reading into the history of the human witness of polar lights opened up dozens (literally) of potential future topics. I have never seen the dancing sky and I have always envied those whose eyes have been bombarded with excited photons. Learning about some of the famous storms of the recorded past and the mythologies of our distant ancestors, my desire to encounter the Northern Dawn is supercharged.
Expect more on polar lights in the future, as the auroras are calling!
Let us end this missive with enchanting imagery. These photos and videos are incredible!
Further Reading and Exploration
Northern lights (aurora borealis): What they are and how to see them – Space.com
Northern Lights Centre – official website
OVATION Auroral Forecast – Space Weather Live
AURORA – 30 MINUTE FORECAST – NOAA