(CNN)Don't be surprised if you find your neighbors turning off their lights for a full hour Saturday night. They're taking part in a global movement called Earth Hour.
How did it start?
Earth Hour is an annual tradition in which people switch off their lights to spread awareness about sustainability and climate change. Started by the World Wildlife Fund, it takes place on March 27 from 8:30 p.m. to 9:30 p.m. local time. (And it's not to be confused with Earth Day)
When did it start?
The symbolic effort started in 2007 in Sydney, Australia, when the WWF encouraged 2.2 million people to turn off their lights for one hour to support action on climate change.
Since then, millions of people around the world have taken part. Landmarks such as the Eiffel Tower, Big Ben, Sydney Opera House, the Empire State Building, Buckingham Palace, the Colosseum and Edinburgh Castle also have gone dark for an hour.
What is it intended to do?
It's meant to bring together people who share one common goal: an ecofriendly future.
How can people get involved?
Organizers suggest you participate in the blackout and sign a petition demanding that political leaders take action to save the planet. The website also has a host of other actions people can take to help ease climate change.