For Katrina Ince-Lum, the countdown to this summer's total solar eclipse has been on since December 2012.

That's when the Canadian travelled to her native Australia to catch her first solar eclipse, an event often touted as "life-changing."

But in a cruel twist of fate — and to Ince-Lum's extreme disappointment — on a mostly clear day, a rogue cloud drifted in front of the sun right at totality, when the moon covered the disk of the sun.

But now, she's getting a second chance.

On Aug. 21, a total solar eclipse will take place across the continental United States, the first in 99 years. It's an event dubbed the "Great American Eclipse."

And Ince-Lum, of Toronto, is ready.

"I've been planning it for a while and I'm really looking forward to it," she told CBC News. "It's a phenomenon that they say is life-changing."

Like many Canadians, Ince-Lum will be travelling to the United States to capture the rare and unique event.

The path of totality stretches from Oregon to South Carolina. In those states, millions of people will experience approximately 2½ minutes of darkness in the middle of the day.

Ince-Lum, an amateur astronomer for the past 20 years, intends to enjoy the experience without any telescopes or fancy equipment.

"I'm not going to do anything particularly complicated," she said. "I just want to enjoy the experience.... I'm just going to sit in my chair and look at it, safely of course."

What is a total solar eclipse?

Though there are other types of solar eclipses — partial and annular, for example, where only part of the sun is covered — nothing compares to a total solar eclipse.

As the moon covers the sun's bright light, its corona — or outer atmosphere — becomes visible.

The sun's corona, seen here during a solar eclipse on Ternate island, Indonesia, on March 9, 2016. (Beawiharta/Reuters)

Somewhere on Earth, there is a total solar eclipse about once every 18 months through a strange scientific fluke. By chance, the moon, at an average distance of about 386,000 kilometres from Earth, just happens to be the same size in the sky as the sun, which is at an average distance of 149.6 million kilometres.

Every so often, it all lines up and, as the moon orbits Earth, it passes in front of the sun, blocking it out entirely.

One of the most anticipated sights is something called Baily's beads. This effect is created around the moon as sunlight travels through mountains and valleys on the moon's surface.

When darkness descends, it will likely give those in the shadow of the moon an eerie feeling: darkness during the day. Birds and other animals will begin their twilight routines, believing that night is about to settle in.

"It'll be dark enough that you'll have difficulty reading print on the page," Paul Delaney, an astronomer and professor at York University in Toronto, told CBC News.

"But all of the bright stars come out; it's twilight. You'll begin to see Venus and Jupiter…. But to have this black disk in the sky surrounding by the white halo, the corona, and all the stars and planets around, it really is an awe-inspiring feeling."

Canada's partial solar eclipse

About 200 million people are within one day's drive of the path of totality, Martin Knopp, associate administrator at the office of operations of the U.S. Department of Transportation, said at a recent NASA news conference.

In Canada, there's the chance to enjoy a partial eclipse, with the moon covering the sun anywhere from 89 per cent in Victoria to 13 per cent in Resolute, Nunavut.

Try very hard to sit back and enjoy the experience. - Paul Delaney

When the eclipse begins, you'll barely notice it. But then you'll begin to see that it looks like someone took a bite out of the sun, in roughly the 1 o'clock to 4 o'clock positions, depending on your location. From there, the moon will slide across much of the lower half of the sun, blocking out its light.

But never look directly at the sun without proper protection: you can seriously damage your eyes.

Try to obtain special eclipse glasses, which you may find at local science stores or science centres. Do not look at the sun, even if a sliver of it is visible

The total solar eclipse on Aug. 21 will cross the continental United States. (CBC News)

"Just because 80 per cent of the sun is missing, 20 per cent of the sun is there. You only need a fraction of a per cent of the sun to be visible to generate eye damage," Delaney said.

"It's not safer today than it is on eclipse day in Canada unless you have the appropriate precautions: that means solar safety glasses…. It doesn't mean wearing two pairs of sunglasses."

Numerous events are taking place across the country, including at universities or local astronomy clubs like the Royal Astronomical Society of Canada. Many locations will have telescopes with special solar filters or solar glasses to give away. There's even a way to watch an eclipse by making a pin-hole camera.

"Try very hard to sit back and enjoy the experience," Delaney said. "It really is wonderful."

That's exactly what Ince-Lum plans to do.

"I want to look around me, see what my friends are doing, observe what the people are doing and just see how the sky changes, how the light changes. I just want to soak it all in."