Earth Hour practice session.

by Brook Wilkinson

Spread the word to all your city-dwelling, stargazing friends: On Saturday night, the ambient light from more than 100 U.S. metropolitan areas will go dim for one hour, starting around the world at 8:30 p.m. local time. The Empire State Building will fade to black. So will the Vegas strip, the Sears Tower, the St. Louis Arch, even the Pyramids and Sphinx in Egypt (thanks, Abercrombie & Kent), the Eiffel Tower, and the Sydney Opera House.

Earth Hour is an initiative introduced by the World Wildlife Fund back in 2007. It's not meant to produce a real reduction in our carbon footprint--we'll have to do a lot more than turn out the lights for 60 minutes to accomplish that--but as a symbolic act that unites millions of people across the globe.

And many hotels are participating. The Conrad Centennial Singapore will have a fleet of hybrid taxis available for guests. Bushmans Kloof, a wildlife reserve in South Africa, will serve dinner by candlelight. At last count, the list of chains pledging to turn off all the (non-essential) lights included Fairmont, Hilton, InterContinental, Langham, Loews, Radisson, and Starwood. So if you're heading into Ducca at the San Francisco Westin for a late dinner on Saturday night and the lights go dim, don't blame it on a breakdown of the country's 19th-century power grid (Obama's got it handled--check out the cover story in the current issue of Wired.)

More than 2,400 cities in 82 countries have pledged to turn the lights off this Saturday. You can do the same at earthhourus.org.