WASHINGTON (CBSDC/AP) — Washington’s National Cathedral is among the landmarks across the globe that plan to turn out their lights for Earth Hour.

The cathedral’s lights are to be dimmed at 8:30 p.m. Saturday as part of the event organized by the Washington-based World Wildlife Fund.

The National Aquarium in Baltimore also plans to participate in the event designed to raise awareness of environmental sustainability issues.

Major cities across the U.S. will be participating, from New York City’s Times Square to the Las Vegas Strip, and from the country’s tallest building to Girl Scout Troop 1174.

The event begun in 2007 encourages people to turn off lights at 8:30 p.m. local time on Saturday. The World Wildlife Fund says people in 135 countries participated last year.

The WWF says challenges us to employ the “I Will If You Will” tactic with your loved ones, or  “dare anyone (your Facebook friends, co-workers, celebrity crushes) to accept your challenge and help protect the Earth or accept the challenge of someone else.”

To see a collaborative effort from countries in past years, watch the video below:

(TM and Copyright 2012 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2012 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)