Tens of thousands of Canadians are expected to flip the main breakers in their homes and businesses tonight, turning out the lights and eliminating their energy use for one hour in recognition of Earth Hour.

The event started in Sydney last year when icons like the Sydney Opera House and Harbour Bridge went dark. It has since become a global movement with the goal of making the world's energy consumption spike downward for one hour as proof that small actions can make a big difference.

In Canada, about 55,000 people have signed up, putting us ahead of Australia and just behind the U.S. They will be taking part in a wide range of events and celebrations, from small intimate, candle-lit dinners to larger-scale, outdoor acoustic jam sessions in city centres, all between 8 and 9 p.m. tonight.

But there's potential for a much larger number of Canadians to take part, with a recent poll suggesting 70 per cent of Canadians will be turning out the lights tonight to mark the event in some fashion.

Plans are in place to celebrate the environmental event across the country/

Toronto's Ontario Science Centre is "into Earth Hour big time," according to Christine Crosbie, media relations officer.

The OSC's free outdoor party will offer up telescopes and astronomy experts to help participants view the heavens and participate in a star count.

An Ojibwa storyteller will also be on hand to lend the event some old-fashioned, electricity- and technology-free entertainment value.

"We're really very excited about this, especially since there's going to be clear skies in Toronto," Crosbie told CTV.ca.

The iconic CN Tower, which was recently outfitted with new LED lights that provide dazzling nightly light shows on the world's tallest free-standing structure, will dim its glow.

Irene Knight, manager of public relations for the tourist attraction, said "green" events like Earth Hour are a priority for the CN Tower. In fact, she said, the new lighting was installed partly because it was projected to be more energy efficient than the previous lighting system.

The tower, which is usually lit up like a giant glow-stick after dark, will be dark except for the aviation lights that serve as a warning to aircraft.

"At this time in the spring the CN Tower is dimly lit for bird migration, but during Earth Hour we will turn off all of our exterior lights except for the aviation lights," she said.

Though the tower's restaurant will remain open, heating will also be turned down at the tower, computer monitors will be turned off wherever possible and elevator frequency will be at a minimum.

In Halifax, the Pier 21 immigration museum will be closed, but will also be taking small steps to observe the event. Communications manager Stefanie Angelopoulos told CTV.ca the facility will be shutting off all unnecessary lights and computer monitors in an effort to reduce energy consumption.

"The museum is going to be completely shut down," she said. "It's closed down anyway at that hour but we're going to make sure that anything that can be shut down will be shut down."

Vancouver Mayor Sam Sullivan kicked off his city's participation on Friday. Vancouver will be powering down, with all City, BC Hydro and Vancity buildings shutting down for Earth Hour.

The event is also being observed in Montreal, Edmonton, Halifax and St. John's, and many small and large communities in between.

Julie Langer, of World Wildlife Fund Canada -- the group organizing the event in Canada -- said the goal of Earth Hour is to inspire action and promote change.

"Earth Hour is a way worldwide for people, businesses to express their deep concern for the planet and about global warming and to really send a message that we have very high expectations for action," she said on CTV's Canada AM.

Langer said most people realize that simply turning off the lights for an hour won't save the planet. But the hope is that by doing so, people will become motivated to "make every hour Earth Hour."

She also said there is something special about participating in a global movement, where one can literally watch the lights go off as their neighbours take part.

"What I think this will give people is a spirit of participation in something that is not just themselves, it's global," she said.