Night skies data report: Photometric assessment of night sky quality at Katahdin Woods and Waters National Monument
Olstad TA , Meyer E, Hung L. 2025. Night skies data report: Photometric assessment of night sky quality at Katahdin Woods and Waters National Monument. Science Report. NPS/SR—2025/299. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2313093
This report characterizes night sky conditions in Katahdin Woods and Waters National Monument (KAWW) 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 two sites—Katahdin Viewpoint and the Overlook—on August 27 and August 28, 2022. NSNSD also used satellite data from 2022 to create a map of predicted night sky conditions in and around the park. The sky overhead remains remarkably dark, with an average zenith brightness of 21.48 mag/arcsec2. We estimate that more than 93% of stars were still visible most of the time, providing one of the best opportunities in the Eastern United States to observe the natural sky. The whole sky over KAWW is just 10%–19% (mean = 15%) brighter than average natural levels, indicating excellent dark sky conditions on average. In KAWW, the average naked eye limiting magnitude (NELM) is 7.05, which indicates an ability to see very faint astronomical features under good seeing conditions and with proper ocular adaptation to darkness. Sky Quality Meter (SQM) measurements average 21.52 mag/arcsec2, indicating that the zenith is darker than we can accurately measure with an SQM. Based on the visibility of astronomical objects, NSNSD classifies the sky as Bortle Class 2: typical truly dark site. As described by Bortle, “Airglow may be weakly apparent along the horizon. M33 is rather easily seen with direct vision. The summer Milky Way is highly structured to the unaided eye, and its brightest parts look like veined marble when viewed with ordinary binoculars.” The main impacts on KAWW’s night sky quality are light domes from Patten, Millinocket, Bangor, and possibly from Quebec, observed along the horizon.
- Type
- Published Report
- Authors
- Olstad, Tyra; Meyer, Erik; Hung, Li-Wei
- Date of Issue
- 2025-05
- Publisher
- National Park Service
- DOI
- 10.36967/2313093
- Units
- KAWW , NRSS , NSNN
- Keywords
- brightness, light pollution, night skies, night sky, photometric assessment, sky quality