Challis Astronomical Observatory
The Challis Astronomical Observatory (CAO) is located in central Idaho (44° 29’ 54” N, 114° 20’ 2” W) five miles west of Challis at 7103 feet (2165 m) elevation in a mountain desert micro-climate that enjoys the driest 5” yearly precipitation) and clearest nights in the state. CAO is located in a very low population region as can be appreciated on the iconic “USA at Night” image. East of the very large River of No Return Wilderness, the region has very low light pollution and hence very dark skies. In nominal winter conditions the Wilderness mountains intercept the weather, making for unusually low snow loads and routine observatory access for maintenance purposes, even in January-March. Over five years we have monitored sky conditions for ~ 1200 nights. CAO experiences completely clear skies 55% of nights, with some cloud cover for another 25%, and 20% mostly cloudy.