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What is the Aurora Borealis?


Mark Robinson, meteorologist
January 15, 2013 — Most sky watchers know what the Northern Lights look like as they shine brilliantly in the night sky, but how are they created? Understanding the auroras begins with the sun.


Some legends make the Northern Lights into something dangerous that you must be careful never to breathe in.
Some legends make the Northern Lights into something dangerous that you must be careful never to breathe in.

“If you whistle at them, they’ll dance better for you,” the Inuit woman explained as I stood there in the middle of the frozen darkness in the hamlet of Tuktoyaktuk, on the Arctic shores of the Northwest Territories. 

She then proceeded to do just that, and as the warbling sound echoed across the vast tundra, it brought to my mind lost days of myth and legend as the green and red curtains shimmered and danced far overhead.

The Inuit have a close relationship with the Northern Lights, which most often appear in their spiritual practices as either the souls of ancestors dancing in the sky, or something to be feared and respected.  Some legends actually make the Northern Lights into something dangerous that you must be careful never to breathe in.

Astrophysicists, however, have a very different view.

In the language of science, the Lights are known as the auroras. There are two sets; the aurora borealis (the Northern Lights) and the aurora australis (the Southern Lights).  

The fact there are two sets gives a clue as to the origins of the aurora.

There are two sets of auroras; the aurora borealis (the Northern Lights) and the aurora australis (the Southern Lights).
There are two sets of auroras; the aurora borealis (the Northern Lights) and the aurora australis (the Southern Lights).

Understanding the auroras begins with the sun. 

At the centre of the solar system, our star generates charged particles in its outer shell (the corona) and these stream towards the Earth as cosmic rays. As the particles begin to interact with Earth’s magnetic field, they are deflected towards the north and south poles by the magnetic field lines. These lines are the reason a compass needle points to the north.

The orientation and shape of the field ensures that the particles will penetrate deepest into the atmosphere at either pole, in a ring pattern that surrounds the magnetic pole. This pole does not always coincide with the geographic or “true” pole, which is why the auroral oval seems to have a lopsided orientation with respect to the planet.

The shape and colours of the aurora are probably the most fascinating aspects of the Lights. Standing under the clear, cold sky in the Canadian Arctic and watching the Lights spin, dance and vortex while changing hue made me think of cloud formations near a summer storm. The colours and patterns are fascinating, but they aren’t random.

The colours of the aurora are varied, but are specific to the chemical makeup of the atmosphere. The most common colour is green and is produced by the interaction of the sun’s charged particles with high altitude oxygen (80 km up).

Blue or red lights characterize nitrogen interactions, while oxygen interactions are green or brownish red depending on how much energy is absorbed.  These colours also vary depending on how high up are the interactions between the cosmic rays and the atoms. 

The dancing or streaming effects are caused by the constant shifting of the streams of magnetic and electrical energy as they move through and around the earth.  This shifting moves the cosmic rays and they can take on patterns that look like swirls, curtains, or streams of water.

And yet, despite the fact that we understand almost exactly what causes them, standing in a frozen Arctic night out on the tundra, I looked up with a sense of awe and wonder and thought maybe, just maybe, something truly mystical was dancing in the sky above my head.

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