YozoraAtlas

How dark is the sky in Washington?

Sky darkness for 64 towns and parks in Washington, worked out from NASA satellite images of light at night (2025). 41 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Chelan National Forest (21.78, Bortle 3), the brightest Seattle (17.43, Bortle 8). Milky Way season in Washington runs May to July: on moonless nights the bright core stands clear of the horizon, climbing to about 15° at its highest.

19 Bortle class, 1 pristine to 9 city center park or dark-sky place city

Numbers like 21.95 or 16.97 are the brightness of the sky overhead on a clear, moonless night, in mag/arcsec². The scale runs backwards: a lower number means a brighter sky, from about 22 for a natural sky to about 17 in a city center.
How the readings are made

All 64 places in Washington

Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Alta Lake State Park4Beacon Rock State Park4Bellevue8Bellingham7Bogachiel State Park4Burien8Cape Disappointment State Park4Chelan National Forest3Columbia National Forest4Colville National Forest3Conconully State Park4Crawford State Park Heritage Site4Everett8Federal Way8Federation Forest State Park4Fort Columbia State Park4Fort Flagler Historical State Park4Fort Simcoe4Gifford Pinchot National Forest4Ginkgo Petrified Forest State Park4Hanford Reach National Monument5Kennewick8Kent8Lake Chelan National Recreation Area3Lake Easton State Park4Lake Roosevelt National Recreation Area4Lake Wenatchee State Park4Lakewood8Leadbetter Point State Park4Marysville7Moran State Park4Mount Baker National Recreation Area4Mount Baker-Snoqualmie National Forest4Mount Pilchuck State Park4Mount Rainier National Park4Mount Spokane State Park4Mount St. Helens National Volcanic Monument4North Cascades National Park4Okanogan-Wenatchee National Forest3Olympia7Olympic National Forest4Olympic National Park4Pacific Pines State Park4Palouse Falls State Park4Rainbow Falls State Park4Rainier National Forest4Redmond8Renton8Richland7Rockport State Park4Ross Lake National Recreation Area4San Juan Islands National Monument5Seattle8Shoreline8South Hill7Spokane8Spokane Valley8Steamboat Rock State Park4Sun Lakes-Dry Falls State Park4Tacoma8Vancouver8Wallace Falls State Park4Washington National Forest4Yakima8