The Washington National Cathedral is among the landmarks worldwide that will observe Earth Hour. (Nikki Kahn/The Washington Post)

The cathedral’s exterior lights will be dimmed at 8:30 p.m. for the annual, world-wide event, which tries to raise awareness of energy issues, reports the Associated Press.

Earth Hour organizers encourage people, businesses and cultural sites to turn off their lights for one predetermined hour, 8:30 to 9:30 p.m. local time.

Millions of people have participated since the first official Earth Hour was held in 2007 in Sydney.

The District has traditionally participated in the event on a municipal level only. While it’ll be lights out at the National Cathedral, the monuments will remain illuminated. This is done for safety reasons, according to the Department of the Interior, which controls the monuments.

The National Aquarium in Baltimore also plans to participate.

Organizers report that people in 135 countries participated last year.

Tell us: Will you observe Earth Hour this Saturday?