This Saturday night, energy-conservation, wildlife, and astronomy groups around the world have a plea for each of us: Turn out the lights! March 28, 2009, from 8:30 to 9:30pm, marks the second annual Earth Hour, a global exercise in saving energy and recalling the natural night sky. During that rolling hour participants worldwide will dim nonessential outdoor lights, look around, and consider how we waste electricity, often produced by burning fossil fuels.

Reducing light pollution is a quadruple win. It’s one small step against global warming. It’s good for sleep and health; circadian disruption may abet a slew of ills, from cancer to depression. It restores essential nocturnal habitat for many creatures, from plankton to moths to migrating birds. And it restores the glories of the night sky, humankind’s original source of wonder and inspiration.

To learn more about these effects, see Seattle Met’s big story on light pollution, Seattle’s worst light trespassers, and how your correspondent actually saw the Milky Way over Green Lake.

During last year’s Earth Hour 2.7 million Chicago-area residents trimmed their juice use by 7 percent and saved 818 megawatts, according to the Cascade Sierra Club, a sponsor of this year’s Seattle Earth Hour. But "Seattle made only a modest effort to turn out the lights during Earth Hour 2008. This time as an officially participating city we hope to do better."

Alas, this weather’s not made for skywatching; Saturday’s forecast is cloudy with a chance of rain. So you won’t likely see the Milky Way. But you can still discover the joys of cutting glare and saving kilowatts.