Using CCD Imagery for the Study of Night Sky Brightness in a Small College Setting

The National Park Service (NPS) Night Skies Team has utilized charge-coupled device (CCD) imagery to create all-sky mosaics of the night sky-brightness at various sites within U.S. National Parks. This data, publicly available on the Night Sky Monitoring Database, applies the imaging and analysis techniques commonly used in the undergraduate astronomy curriculum, but in a new context. We sought to reproduce the methods of Duriscoe, Luginbuhl, & Moore (2007) in the context of a burgeoning astronomy research program at a small liberal arts college. Our goals are to make datasets that can be utilized by policy makers and advocates of dark sky preservation in the Salt Lake Valley, and to create publicly available code for similar projects to be reproduced by other astronomy students, at a fraction of the cost of the NPS methods. We have used a CCD camera to image the night sky from locations near Salt Lake City, using typical equipment available to a small college astronomy program. After calibrating and aligning all of the images, we created a panoramic view of the night sky in Python. This map of sky brightness in magnitudes per square arcsecond can be used to determine a number of indices of sky quality: surface brightness at notable locations (zenith, brightest, darkest portions of the sky), total integrated sky background, and total integrated brightness of a nearby city's light dome. Our procedures and Python scripts are publicly available on GitHub [https://github.com/jrka/slclight/] for other small college or amateur researchers to use. By investigating the challenges of applying this technique in a small college setting, we have aimed to make the study of night sky brightness easily accessible to other researchers. We encourage other undergraduate astronomy programs to utilize this procedure in their advanced laboratory courses or independent research in order to help teach CCD imaging techniques. The resulting datasets have personal significance for the students and interdisciplinary applications to policy, ecology, and human health.