Earth Hour starts at 8:30 pm Saturday night wherever you are: turn off your lights and celebrate.

“Earth Hour is the largest mass participation event in the world’s history. Ever.” Wow—if you think about it, it’s true. “It’s not about what country you’re from—it’s about what Planet you’re from.” Check some before/after photos here.

The official video:

First silly, since everyone loves silly arty fun:

Lights on:

Turn the lights off:

What is Earth Hour? Well, again, for a second year, it’s a trending topic on Twitter—meaning the world is abuzz about it. It’s a planetary happy hour, a day that’s fast overtaken Earth Day itself as a treasured, token, symbolic and fun moment to look at the world through new, candle-lit vision.

It started in Sydney only a few years ago, back in 2007:

Then, in 2008, it went global. Only, it didn’t catch fire everywhere, not even in our “green” minded hometown, Boulder. Our video, via Alex King:

Earth Hour – Boulder, Colorado from Alex King & Mito Media on Vimeo.

But last year it went nuts. It inspired lots of fun dinner parties and dark skyscrapers and crazy news coverage and, the true mark of anything huge and popular, some cynicism.

Excerpt re today:

…Europe’s best known landmarks — including the Eiffel Tower, Big Ben and Rome’s Colosseum — fell dark Saturday, following Sydney’s Opera House and Beijing’s Forbidden City in joining a global climate change protest, as lights were switched off across the world to mark the Earth Hour event.

In the United States, the lights went out at the Empire State Building in New York, the National Cathedral in Washington, D.C., and the Coca-Cola headquarters in Atlanta, among many other sites in the Eastern time zone.

Millions were expected to turn off lights and appliances for an hour from 8:30 p.m. in a gesture to highlight environmental concerns and to call for a binding pact to cut greenhouse gas emissions. This year’s was the fourth annual Earth Hour, organized by the World Wildlife Fund.

“I think it’s great to see that hundreds of millions of people share this common value of lowering our carbon footprint,” said Dan Forman, a spokesman for WWF in Washington.

Some 4,000 cities in more than 120 countries — starting with the remote Chatham Islands off the coast of New Zealand — voluntarily switched off Saturday to reduce energy consumption, though traffic lights and other safety features were unaffected, organizers said.

“We have everyone from Casablanca to the safari camps of Namibia and Tanzania taking part,” said Greg Bourne, CEO of WWF in Australia, which started Earth Hour in 2007 in Sydney before it spread to every continent.

Other sites expected to participate in the U.S. were businesses on the glittering Las Vegas strip and the Mount Rushmore presidential monument in South Dakota. The lights stayed on at the U.S. Capitol and the Lincoln and Washington monuments.