Ruth Ann Chicoine, the Canadian Space Agency's national project manager for AuroraMAX, said a spot on the sun exploded Tuesday in what is known as a solar flare and sent out a sort of storm cloud called a coronal mass ejection.
Such storms collide with particles and gases in the Earth's atmosphere to create the northern lights, also known as the aurora borealis.
The solar storm was expected at around 3 a.m. EST Thursday, but Chicoine joked Thursday afternoon that it appeared to be "taking the panoramic route to Earth." The storm was finally spotted on its way at 2:32 p.m. EST Thursday.
"The good news is if the storm is actually (tonight), it might make for some spectacular conditions tonight to see the northern lights," she said in a phone interview from Saint Hubert, Que.
The auroras form in an oval above the North and South poles, Chicoine explained. In the northern hemisphere, a solar storm stretches the oval down towards southern latitudes and that's when the lights can be seen in such places as southern Ontario.
Chicoine said it's always tough to predict when solar storms will hit.
"Aurora scientists like to joke that aurora prediction is even less reliable than weather predictions ... It's hard to do," she said.
"We can't pinpoint exactly when this will hit us. We can't pinpoint exactly where the northern lights will be visible. But we can give a general idea. (On Wednesday), AuroraMAX issued a nationwide aurora alert, meaning that areas of the country in the southern regions, as far right down to the northern U.S. states, would be able to see the northern lights if this storm hits the way that we were predicting."
There hasn't been a northern lights phenomenon like this in a year or two, she said.
The best viewing was expected in darker places, such as rural areas. People in cities could have difficulty because of lights from buildings or street lamps.
Sky-watchers not wanting to go out in the cold or not able to get to a dark enough area weren't out of luck. AuroraMAX — which is a partnership between the University of Calgary, the City of Yellowknife, Astronomy North and the Canadian Space Agency — live streams the northern lights every night from Yellowknife on the websites www.asc-csa.gc.ca/eng/astronomy/auroramax/connect.asp and http://astronomynorth.com/auroramax
Chicoine said people who want to see "really cool" video of Tuesday's solar flare erupting can go to www.youtube.com/watch?v=tSA2dQT5DjI or www.youtube.com/watch?v=7Mz2laHjVoQ#t=181 to see a good animation of how solar storms fuel the northern lights.
The website http://helios.swpc.noaa.gov/ovation/North_New.html also has a real-time position of the auroral oval, which can help people find out where they're most likely to view northern lights.
"When we see an aurora in the south of Canada, and even sometimes in the North, that aurora can actually be located 800 to 1,000 kilometres away," said Chicoine. "They're structures that can be up to 300 or 400 kilometres high, so even if you see that the oval is not that close and it's not directly over your head, you still may want to keep an eye on the skies."