The first ever Earth Hour was in 2007, in Sydney, Australia. After it happened (and went well; around 2.2 million people took part), they wanted to make it a national event: but internationally, cities were beginning to sign up to take part in the 2008 Earth Hour. Earth Hour has only continued to get bigger, with more and more cities worldwide participating.
The website, www.earthhour.org, gives a history of this; and also has other Earth-friendly challenges in which you can participate. There is also a website: www.beyondthehour.org, which talks more about participating countries and the history, and also why Earth Hour is so important. If you want to do Earth Hour, the next one is scheduled for March 29th, at 8:30. However, not using electicity for an hour or two is easy enough to do every week. If you want to make a difference, both participate in and out of Earth Hour by turning off your electricity, and spreading the word about Earth Hour. Maybe, someday, Earth Hour will be a time when the whole world turns off all their electricity and takes a moment to think about how they can help improve our planet.
Information Sources:
http://www.earthhour.org/
http://www.beyondthehour.org/
Picture Source:
http://www.torontosun.com/2013/03/24/chris-hadfield-captures-earth-hour-from-space
(This source has pictues that Chris Hadfield took from space during this year's Earth Hour, including the one on this post. I recommend checking the pictures out!)