Earth Hour has already passed for Asia and Australia. For the Middle East and Africa, it's hours away. For North America and Europe, there is plenty of time to prepare for Earth Day. (This article was written at 9:30 a.m. EDT).

Earth Day is celebrated on March 26, 2011 at 8:30 pm to 9:30 pm local time. During that hour, households and organizations are encouraged to turn off all non-essential lights and other uses of electricity.

The idea is to raise awareness about reducing the carbon footprint and light pollution and encourage participants to go beyond the hour - or practice Earth Hour principles for the other 8,000+ hours of the year.

Earth Hour was conceived in 2007 by Australian newspaper The Sydney Morning Herald and the World Wide Fund for Nature (WWF).

Beyond shutting off lights for 1 hour on March 26, there are other ways of participating and showing support. The official Earth Hour website, www.earthhour.org, lists several ways.

Twitter users can show support by installing an application at www.eh2011.com that shuts off the lights in the users' profile picture during Earth Hour.