Why the northern lights have been lighting up southwestern Ontario skies, and how you can see them tonight

Sightings of the northern lights — known as the aurora borealis — have become an increasingly common topic of discussion for people in southwestern Ontario this year, with social media feeds periodically becoming flooded with photos of mesmerizing green and pink hues in the night sky.

According to a local astronomer and a professor at Western University in London, the increase in auroral activity is thanks to the sun's natural cycle, which culminates in a period of increased activity about every 11 years.

"The sun's activity has definitely increased in the past year. It's actually higher than it's been in more than 20 years," said Jan Cami, also the director of the university's Hume Cronyn Observatory.

The aurora borealis is caused by solar particles that are flung from the sun toward the Earth by an explosion of energy on the sun's surface called a coronal mass ejection (CME).

"[That energy] travels a few hundred kilometres a second until it reaches Earth," said Cami. "There's a whole mess of charged particles that impact the Earth's magnetic field."

The distinct colours in the aurora are caused by those particles interacting with elements in the atmosphere.

When the sun's 11-year cycle comes to a close, it reaches what's called solar maximum — a state in which events like solar flares and CMEs are significantly more common due to changes in the sun's magnetic field. Activity increases as the solar cycle progresses, moving closer to solar maximum, and then slows down on its way to the other end of the cycle known as solar minimum.

"We're approaching the maximum," said Cami. "We may have already reached the maximum, but we won't know until eight or so months after it happens because of the way these things are measured."

According to the U.S. National Oceanic and Atmospheric Agency (NOAA), a severe geomagnetic storm was underway as of 1 p.m. on Thursday and the likelihood of northern lights being visible in southwestern Ontario is high.

"Millions of people enjoyed the solar eclipse without necessarily knowing all the science behind it. I think it's the same for northern lights, whether or not you understand what's happening. I go out not as a scientist, but as a human being who likes to experience this," Cami said.

Craig Levine is a former national president of the Royal Astronomical Society of Canada and a longtime member of the London Centre of the Royal Astronomical Society of Canada. He's also an amateur astrophotographer who hopes to capture some of the ethereal tapestry in the sky.

"It's better than any fireworks display you'll ever see," said Levine, adding the wonder light show builds over time.

"You tend to look toward the north, first, and you'll see a greenish hazy glow on the horizon. Then, the colours intensify, and you'll see greens, reds, and some oranges. For bigger storms like this, you can sometimes see big, shimmering sheets as the aurora moves overhead and all around."

For those hoping to see the aurora on Thursday or Friday night, both Levine and Cami have similar advice — find somewhere that's far from the city lights, and dress for cooler temperatures. Levine said it's important to be patient, and Cami advised that forecasts can sometimes be inaccurate.

According to NOAA, the best time of day to see the lights is often between 10 p.m. and 2 a.m.

Levine said perhaps the best way to enjoy the lights is to share the experience with others.

"There's so much division right now, but we all share the night sky, and that's a wonderful thing to bring people together."