Night skies data report: Photometric assessment of night sky quality at Cumberland Island National Seashore

White, Kelsey

doi:10.36967/2313314

This report characterizes night sky conditions in Cumberland Island National Seashore (CUIS) 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 one site. These ground-based observations were collected on the night of March 9, 2018. Satellite data from 2023 were used to create a map of predicted night sky conditions in and around the park. The sky overhead is influenced by moderate light pollution with a single measurement zenith brightness of 20.86 mag/arcsec2. We estimate more than 43% naked eye stars were visible throughout the data collection period, providing an opportunity to partially view the natural night sky from the park during a cloudless, moonless night. The whole sky over CUIS is 416% brighter than natural levels, indicating that natural night sky conditions are not readily visible, on average. In CUIS, we classified the sky as Bortle Class 4: rural/suburban transition, based on the visibility of astronomical objects. Our Sky Quality Meter (SQM) recorded a single measurement of 20.77 mag/arcsec2, indicating a quality of moderate condition. Obvious light-pollution domes are apparent over population centers in several directions. The zodiacal light is evident but does not extend halfway to the zenith at the beginning or end of twilight. The Milky Way well above the horizon is still impressive but lacks all but the most obvious structure. The main impacts on CUIS’s night sky quality were the light domes from St. Marys, Jacksonville, Yulee, Kings Bay Base, Fernandina Beach, Kingsland, Brunswick, St. Simons, Jacksonville Beach, and Savannah.

Night skies data report: Photometric assessment of night sky quality at Cumberland Island National Seashore

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