BORTLE CLASS 4 / SKY KEY
Rural / suburban transition
Still a useful stargazing sky, with more obvious light domes and less contrast on faint diffuse objects.
4
HOW TO READ IT
One number is a sketch of the sky, not the whole night.
A Bortle class describes what the sky looks like under particular conditions. Walk across a large park, turn toward a town, add snow or smoke, and the view can change. Use the number to compare darkness quickly, then read the stop page for the horizon, headlights, access and everything else that decides whether the place actually works.
Colorado stops currently logged as Bortle 4
Aspen Mountain SundeckEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗BoulderBortle 4 is used for the AstroTours.org observing location at Boulder Valley Ranch based on field experience. Bortle is observational, so transparency, snow, moonlight and local light can shift the practical impression. ↗BreckenridgeEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Colorado National MonumentEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Golden Gate Canyon State ParkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Highline Lake State ParkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Jackson Lake State ParkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Mueller State ParkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Old SnowmassEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Ouray KOA Holiday StargazingEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Pine River Library Dark Sky KitsEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Rifle Gap State ParkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Staunton State ParkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗The Nest at Black HawkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗Trinidad Lake State ParkEstimated Bortle 4 from modeled sky-brightness/light-pollution data at the guide location. Bortle is observational, so treat this as roughly ±1 class until field checked. ↗