Night Skies Data Report: Photometric Assessment of Night Sky Quality at Walnut Canyon National Monument
Olastad TA , Hung L, Meyer E . 2025. Night Skies Data Report: Photometric Assessment of Night Sky Quality at Walnut Canyon National Monument. Science Report. NPS/SR—2025/336. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2314893
This report characterizes night sky conditions in Walnut Canyon National Monument (WACA) using measurements made in the park unit and models of regional conditions based on satellite data. The National Park Service (NPS) Natural Sounds and Night Skies Division (NSNSD) collected ground-based observations and obtained calibrated night sky imagery to characterize the night sky at one site—the Rim Trail - East Overlook—on five nights from May 12, 2002 to March 13, 2012. Satellite data from 2023 were used to create a map of predicted night sky conditions in and around the park. The sky overhead remains mostly dark, with an average zenith brightness of 21.68 magnitudes per arcsecond squared (mag/arcsec2). We estimate more than 88.6% of naked eye stars were visible with the sky brightness levels measured throughout the data collection period, providing a decent opportunity to view the natural night sky from the park during a cloudless moonless night. However, the whole sky over WACA is 31%–71% (mean = 49%) brighter than average natural levels, indicating degraded dark sky conditions. Based on the visibility of astronomical objects, NSNSD classified WACA’s sky as Bortle Class 4 (rural/suburban transition). The average naked eye limiting magnitude (NELM) is 6.8, which is approaching the faintest brightness the human eye is able to detect. The main impacts on WACA’s night sky quality are the obvious light domes from Flagstaff and surrounding communities and the greater Phoenix metropolitan area. ious light domes from Flagstaff and surrounding communities and the greater Phoenix metropolitan area.
- Type
- Published Report
- Authors
- Olastad, Tyra; Hung, Li-Wei; Meyer, Erik
- Date of Issue
- 2025-07
- Publisher
- National Park Service
- DOI
- 10.36967/2314893
- Units
- NRSS , WACA
- Keywords
- brightness, light pollution, night skies, night sky, photometric assessment, sky quality