SUNDRE – Many residents have recently been delighted and awestruck by a celestial sight that has captivated the imaginations of people for millennia.
But what from the planet’s surface as observed through human eyes appears to be a mesmerizing display of lights dancing in the night sky, is actually the result of a reaction occurring in the Earth’s upper atmosphere from a constant bombardment of particles from the Sun that arrive in ebbs and flows.
“Anybody who’s seen the northern lights in a big, dancing display is never going to forget it,” said Ian Mann, a physics professor at the University of Alberta.
“It’s absolutely one of the most beautiful things in nature; it’s not surprising that lots of people want to see it,” Mann said late last month during a phone interview.
Providing a layman’s explanation about the nature of the northern lights and why the auroras produce a range of colours from green to red, he told the Albertan they are “caused by the raining down of energetic particles from space into the upper aspects of Earth’s atmosphere.”
Offering a metaphorical analogy to further illustrate the phenomenon, he said, “It’s a bit like the old cathode-ray tubes, where at the back of the TV there was a beam of electrons that would be accelerated and shot and hit the screen.”
As the electrons collide into the screen, different phosphors glow to produce the characterization of the colour picture, he said.
“So, it’s a bit the same for the production of the aurora borealis and aurora australis, in that there’s charged particles – mostly electrons, but sometimes protons – that are raining down along magnetic fields,” he said.
The particles come down guided by the magnetic fields and can reach altitudes between 100 kilometres (kms) upwards of 300 kms before crashing into the atmosphere’s constituents, he said.
“And depending on the energy of the particle as it comes in and the thing it collides with, then the emission and the colours of light that you get are determined by the photons of light that are released by these particles as they decay back down into lower energy states,” he said.
“So, it’s a bit like hitting the old cathode-ray television screen with a beam of electrons and getting different colours depending on what they hit.”
Solar cycle
As to whether the auroras have been more active of late, with plenty of breathtaking pictures posted all over social media, Mann said we first must look farther out into planetary space toward their source: our sun, which is about 150 million kilometres – or 93 million miles – away.
“There are various types of activity on the sun,” he said, in this instance referring to enormous explosions known as coronal mass ejections.
“They’re very, very large-scale releases of energy from the magnetic fields that kind of poke out of the visible surface of the sun and out into the lower layers of the atmosphere into what we call the corona,” he said.
“Those magnetic fields can release energy explosively and throw out material into space,” he said. “So, if that comes hurtling toward the Earth, then it can transfer some of its energy into near-Earth space, and some of that energy makes its way down into the aurora, producing these kind of dancing light displays.”
In other words, the auroras are associated with more severe types of space weather, he said, adding the more brightly the northern lights illuminate the night sky, the more space radiation was produced by our solar system’s star along with more electro-magnetic disturbances whose interactions can be “less pleasant.”
“The number of those explosions on the sun follows what’s called a solar cycle” that follows changes in the sun’s magnetic environment, which he characterized as “quite dynamic.”
The sun’s primary polarity reverses from pointing in one direction to pointing in the other direction roughly every 11 years, he said.
“In 22 years, you have a full solar cycle where the magnetic field polarity will reverse and then go back again into its kind of original orientation,” he said, adding complete cycles vary a bit and aren’t necessarily precisely every 22 years.
“But it’s fairly periodic, this variation,” he said.
Earth’s magnetic field is also known to have reversed polarities throughout the planet’s history, but on a much longer geological timescale as indicated by rock records, he said, adding the sun is so large that its time scales are vastly faster.
“This solar wind, as it’s blowing – or these explosions as they arrive – the amount of energy that’s transferred is controlled largely by the relative directions of the magnetic fields,” he said.
“And it turns out that if the magnetic field in the solar wind and the Earth’s magnetic field are oppositely directed, there’s much more energy transfer than if they’re in other directions.”
Additionally, the geometry of the tilt of the Earth’s magnetic field as well as the seasons are factors that play a role in determining how brilliant aurora borealis will appear to be, he said.
Equinoxes generally more active
“There’s a much stronger magnetic coupling around the two equinoxes than there are at the solstices,” he said.
“The spring and autumn equinoxes typically have more energy transfer,” which translates to bigger and brighter northern lights, he said.
Regarding the solar cycle, the number of explosions on the sun and the structure of the magnetic field on its surface also follow the same cycle, he said.
“So, we have this kind of transition from more active times – what we call solar maximum – and then minimum times, which imaginatively is solar minimum,” he said.
Intuitively, a solar maximum is associated with more explosions on the sun, which fuel more space weather and by extension more vibrant northern lights, he said.
“And then, you have the transition between those two states,” he said, describing the ascending phase when activity is increasing, and the opposite descending phase as activity being reduced.
“Right now, we’re in an ascending phase of that solar cycle. So, that’s one of the reasons why the activity is being observed to increase; is we’re kind of projecting along toward solar max,” he said.
“The latest predictions suggest that the solar maximum might be somewhere around July in 2025. So, just over two years from now might be the peak of the current solar cycle.”
Earth’s shield
As beautiful as the auroras may be, they are also a reminder of the formidable power that fuels the sun, which merely evolves according to the laws of physics, he said.
“The magnetic field around the Earth provides a very strong shield against the most energetic particles that come from the Sun,” he said, adding there are other “energetic particles than the ones that we see causing the aurora raining down into the atmosphere.”
Those very energetic and highly relativistic particles associated with these violent events on the sun – such as protons – can be quite hazardous to human health. But Earth’s magnetic field effectively shields the planet’s surface from those particles, he said.
However, as humanity reaches out to the stars with plans to in the coming years put astronauts back on the moon for the first time in decades, such factors could potentially pose a threat to the crews that will be making history, including a Canadian who is part of NASA’s Artemis program.
“We’re going back to the lunar vicinity,” he said. “We’ll be outside of the magnetic shield of the Earth and out in deep space for first time since the Apollo era. That puts the astronauts in a more radiation-risky environment if one of these solar energetic particle bursts were to occur.”
But from the relative safety of Earth’s surface, the rest of us will continue to enjoy the opportunity to see a celestial display unlike any other.
“Down here, we do quite well,” he said. “We get the chance to see the dancing northern lights above us as a benefit. So, that’s not so bad!”
