How dark is the sky in Colorado?
Sky darkness for 44 towns and parks in Colorado, worked out from NASA satellite images of light at night (2025). 26 of them have skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Rio Grande National Forest (21.86, Bortle 3), the brightest Denver (17.10, Bortle 8).
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
Darkest skies in Colorado
- Rio Grande National ForestBortle 321.86
- Dinosaur National MonumentBortle 321.84
- San Juan National ForestBortle 321.82
- Canyons of the Ancients National MonumentBortle 321.81
- Chimney Rock National MonumentBortle 321.79
Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.
Brightest city skies in Colorado
All 44 places in Colorado
Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Arapaho National Recreation Area4Arvada8Aurora8Black Canyon of the Gunnison National Park4Boulder7Broomfield8Browns Canyon National Monument4Camp Hale-Continental Divide National Monument4Canyons of the Ancients National Monument3Castle Rock7Centennial8Chimney Rock National Monument3Colorado National Monument4Colorado Springs8Curecanti National Recreation Area3Denver8Dinosaur National Monument3Dominguez-Escalante National Conservation Area4Florissant Fossil Beds National Monument4Fort Collins7Grand Junction7Great Sand Dunes National Park and Preserve3Greeley7Gunnison Gorge National Conservation Area4Highlands Ranch8Holy Cross National Forest4Lakewood8Longmont7Loveland7McInnis Canyons National Conservation Area4Mesa Verde National Park4Naturita4Norwood4Nucla4Pueblo8Rio Grande National Forest3Rocky Mountain National Park4San Juan National Forest3Silver Cliff4Thornton8Westcliffe4Westminster8White River National Forest4Yucca House National Monument4