The year of the Aurora
On a few occasions this year, people found themselves in one of two categories: those who saw the Northern Lights and those who missed them (and likely only caught them on social media).
The Aurora Borealis lit up the sky across much of North America in May and again in October.
While there were many other nights to see the stunning colours up above, they were particularly vibrant and visible on those occasions with many people able to see them with the naked eye from their own backyard. According to NASA the May 2024 Aurora display was potentially one of the strongest on record in 500 years.
For a basic explanation of what causes the Northern Lights we touched base with Dr. Megan Gillies, PhD, instructor in the Department of Chemistry and Physics.
“We have this massively active star in our backyard,” a.k.a. the Sun. “Our Sun continually streams plasma particles, such as electrons and protons, outward into space - we call this the solar wind.” In addition to the particles, the solar wind also carries the Sun’s magnetic field system outward into space. This steady stream of particles and magnetic fields actually creates a ‘space’ weather system here on Earth. And, as described by Gillies, “Earth is in the way of that wind.”
“Luckily, Earth has its own magnetic field around it,” she explains, likening it to the magnetic field of a bar magnet. In a perfect setting, it would be a symmetrical, spherical field around the Earth outside of the atmosphere. Gillies says the geomagnetic field “acts kind of as a shield around us and it protects us from all of the harmful stuff that is coming from the Sun.”
She explains that the more the Sun blasts out, the more our geomagnetic field kicks into gear and the solar wind and storm is redirected around Earth and continues on into space. In case you are wondering how strong solar winds are, they travel at an average speed of 1.4 million kilometres per hour.
To visualize what happens, Gillies uses the example of a rock in a stream. “You know how the water breaks around the rock and then keeps going but it kind of drags out some water behind? This is exactly what our magnetic field does.”
Essentially, the stronger the storm is, the more our magnetic field (on the side farthest from the Sun) gets pulled down wind, and continues to pull back. Eventually the magnetic field gets pulled farther and farther, stretching like an elastic band. It won’t break, says Gillies, but it will hit a point where it sort of snaps back towards Earth, going back to its original more symmetrical shape.
“When it snaps back it gathers up all of these high energy particles, shooting them down along our magnetic field line where they enter our atmosphere and interact with various atmospheric gasses and particles above us,” she says.
So in short, what we call the Northern Lights, are really just high energy particles interacting with Earth’s magnetic field and atmosphere.
While there is always activity like this from the Sun, it gets more active every 11 years as it approaches and enters its solar maximum period. In October of this year, NASA confirmed the Sun had reached the maximum and said it could continue for the next year.
Gillies says this essentially means that the sun is sending more particles in big streams or chunks that are known as coronal mass ejections. This causes larger space weather storms. The bigger the storm – the further south the aurora can be seen, and the more intense the ‘storms’ are.
So why do we see different colours of lights?
“Depending on what the energy was of the electron or proton coming in and what molecule or atom it hits, that’s what causes those beautiful colours,” says Gillies, who notes that altitude also impacts colour.
“If you were up really high, around 230 kilometres altitude, and you had a low energy particle coming in, that’s where you get those gorgeous, deep reds. It’s taking oxygen molecules and at a certain energy, after those molecules relax, they emit those deep red hues.”
Particles with more energy travel further into the atmosphere to around 110 kilometres altitude and interact with oxygen, emitting the green hue often associated with the Aurora. Those particles that reach 90 kilometres react with nitrogen, says Gillies, explaining that the subsequent emitting of photons is what causes the blue colours.
While it might seem like the Aurora has been out more in 2024, that is not quite the case. “The Aurora is actually always present but we just don’t always see it, maybe it’s not bright enough or maybe we’re just not in a place to see it.” She points out that the two major showings this year were extra visible because the storms that caused them were extremely large. As a result,they were highly visible over a larger portion of Canada and the U.S., even in large cities with a lot of light pollution. Gillies also points out that there is a heightened awareness around when the storms will be visible thanks to social media and Facebook groups like the Alberta Aurora Chasers.
For those looking to catch the next light show, Gillies recommends following a Facebook page like the one above or finding other trackers like the U of A’s Aurora Watch. They, along with groups like NASA, track space weather and can accurately predict when the Aurora will be visible.