Night Skies Data Report: Photometric Assessment of Night Sky Quality at Dinosaur National Monument

Meyer, Erik

doi:10.36967/2314522

This report characterizes night sky conditions in Dinosaur National Monument (DINO) using measurements made in the park unit and models of regional conditions based on satellite data. Calibrated night sky imagery was obtained to characterize the night sky at 4 sites. These ground-based observations were collected on 4 nights from July 15, 2009 to June 13, 2012. Satellite data from 2024 were used to create a map of predicted night sky conditions in and around the park. The sky overhead remains excellent with an average zenith brightness of 21.99 mag/arcsec2. We estimate more than 96.90% naked eye stars were visible throughout the data collection period, providing an outstanding opportunity to view the natural night sky from the park during a cloudless moonless night. The whole sky over DINO is 17%–32% (mean = 21%) brighter than average natural levels, indicating excellent dark sky conditions on average. In DINO, we classified the sky as Bortle Class 3: rural sky, based on the visibility of astronomical objects. A general description of Bortle 3 conditions is “Some indication of light pollution is evident along the horizon. Clouds may appear faintly illuminated in the brightest parts of the sky near the horizon but are dark overhead. The Milky Way still appears complex” (Bortle 2001, p. 01). Under this Bortle condition, the complexity of the Milky Way is characterized by visible dust lanes interspersed with diffuse stellar light. The average naked eye limiting magnitude (NELM) is 6.6, which is approaching near pristine under average conditions. Our Sky Quality Meter (SQM) measurements averaged 21.52 mag/arcsec2, indicating the zenith was darker than what we can accurately measure with an SQM. The main impacts on DINO’s night sky quality, ordered by predicted brightness of light domes, were from Vernal (UT), Maeser (UT), Naples (UT), Salt Lake City (UT), Grand Junction (CO), Provo (UT), Rock Springs (WY), West Valley City (UT), Orem (UT), and West Jordan (UT). Small light domes were observed along the horizon, with a few exceeding the natural brightness of the Milky Way. The most prominent light dome originated from Vernal and Maeser in Utah. All other light domes were relatively small and from distant larger cities or nearby lesser populated towns.

Night Skies Data Report: Photometric Assessment of Night Sky Quality at Dinosaur National Monument

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