AN ABSTRACT OF THE THESIS OF Carsten Christof Grellmann for the degree of Honors Baccalaureate of Science in Mechanical Engineering presented on May 22, 2009. Title: Light Pollution and the Limiting Visual Magnitude in Corvallis, Oregon. Abstract approved: Richard Peterson This study sought to ascertain the degree to which the night sky of Corvallis is affected by light pollution by determining the limiting visual magnitude. Defined as the brightness of the dimmest star that can be seen with the averted naked eye, the limiting visual magnitude establishes a quantitative standard by which to judge the quality of the night sky. Using the star count method and predetermined star fields prescribed by the International Meteor Organization, observations were conducted at Kings Boulevard and Van Buren Street, the Valley Library Quad, and Riverfront Park from the months of November to April. For the purposes of comparison, observations were also conducted at Adair County Park, downtown Portland, and Warm Springs in Central Oregon. This study concluded that the skies of Corvallis are moderately affected by light pollution, with limiting magnitudes between +5.85 and +6.27 with an uncertainty of ±0.12 for the three Corvallis sites, as compared to +7.16 at Warm Springs and +5.04 in downtown Portland. Furthermore, examples of light pollution and its effect on the night sky were photographically documented at each site with a Canon Digital Rebel XT camera and an 8-inch Schmidt-Cassegrain telescope. Key Words: Light Pollution, Limiting Visual Magnitude, Astronomy Corresponding email address: [email protected] ©Copyright by Carsten Christof Grellmann May 22, 2009 All Rights Reserved Light Pollution and the Limiting Visual Magnitude in Corvallis, Oregon By Carsten Christof Grellmann A PROJECT submitted to Oregon State University University Honors College in partial fulfillment of the requirements for the degree of Honors Baccalaureate of Science in Mechanical Engineering Presented May 22, 2009 Commencement June 2009 Honors Baccalaureate of Science in Mechanical Engineering project of Carsten C. Grellmann presented on May 22, 2009. APPROVED: Mentor, representing Mechanical, Industrial, and Manufacturing Engineering Committee Member, representing Physics Committee Member, representing Mechanical, Industrial, and Manufacturing Engineering Dean, University Honors College I understand that my project will become part of the permanent collection of Oregon State University, University Honors College. My signature below authorizes release of my project to any reader upon request. Carsten Christof Grellmann, Author Acknowledgements I would like to thank my mentor, Dr. Richard Peterson, and my committee members, Dr. Kenneth Krane, Dr. William Hetherington, and Dr. Nancy Squires, for serving as excellent resources and encouraging me in this research. Without their expertise and support, this project would not have been possible. I would also like to thank my parents for their support and encouragement in taking on this project, and the contributing members of the Excellence Fund, who generously provided $250 toward the purchase of a camera. Most of all, I would like to thank my sister, Elise Grellmann, for helping me carry my equipment around the city, and keeping me company on those long, cold nights of observing. Even though she irreverently calls star clusters “a bunch of sprinkles.” TABLE OF CONTENTS 1. INTRODUCTION .......................................................................................................... 1 2. BACKGROUND AND LITERATURE REVIEW ........................................................ 3 2.1. Light Pollution ......................................................................................................... 3 2.2. Limiting Visual Magnitude ...................................................................................... 6 2.3. Human Vision and Dark Adaptation ....................................................................... 8 2.4. Previous Star Counts .............................................................................................. 10 3. METHODS ................................................................................................................... 12 3.1. International Meteor Organization Star Count Method ......................................... 12 3.2. Observing Locations .............................................................................................. 14 3.3. Weather Conditions and the Moon ........................................................................ 19 3.4. Photographic Documentation ................................................................................ 19 4. RESULTS ..................................................................................................................... 22 4.1. Kings Boulevard and Van Buren Street ................................................................. 22 4.2. Valley Library Quad .............................................................................................. 24 4.3. Riverfront Park ...................................................................................................... 26 4.4. Adair County Park ................................................................................................. 28 4.5. Central Oregon ....................................................................................................... 28 4.6. Tom McCall Waterfront Park ................................................................................ 28 5. ANALYSIS ................................................................................................................... 29 5.1. Kings Boulevard and Van Buren Street ................................................................. 29 5.2. Valley Library Quad .............................................................................................. 32 5.3. Riverfront Park ...................................................................................................... 35 6. CONCLUSIONS........................................................................................................... 38 BIBLIOGRAPHY ............................................................................................................. 39 APPENDIX A: INTERNATIONAL METEOR ORGANIZATION STAR FIELDS ...... 40 LIST OF FIGURES Figure 1: Light Output from a Street Lamp (Adapted from Macrobert, 1996) .................. 4 Figure 2: Nighttime Photograph of the Kings and Van Buren Observation Site .............. 15 Figure 3: Primary Sources of Illumination around Kings and Van Buren Site ................ 15 Figure 4: Nighttime Photograph of the Valley Library Quad Observation Site ............... 16 Figure 5: Characteristic Sources of Illumination around Valley Library Quad Site ........ 17 Figure 6: Nighttime Photograph of the Riverfront Park Observation Site ....................... 18 Figure 7: Characteristic Sources of Illumination around Riverfront Park Site ................. 18 Figure 8: Tripod Mounted Canon Digital Rebel XT ........................................................ 20 Figure 9: Schmidt-Cassegrain Telescope with Camera Body Mounted to Rear Cell ....... 20 Figure 10: Focal Reducer, T-Adapter, T-Ring, and Camera Mounted to Telescope ........ 21 Figure 11: 10 s, 20 s, and 30 s Exposures of M35 from Kings and Van Buren ............... 23 Figure 12: 10 s, 20 s, and 30 s Exposures of M35 from the Valley Library Quad ........... 25 Figure 13: Limiting Visual Magnitude for Three Corvallis Locations for Typical New Moon to Full Moon Cycle................................................................................................. 26 Figure 14: 10 s, 20 s, and 30 s Exposures of M35 from Riverfront Park ......................... 27 Figure 15: 5 Minute Exposures of Big Dipper Taken from Kings and Van Buren (Top) and Adair County Park (Bottom) ...................................................................................... 30 Figure 16: Ring Nebula photographed from Kings and Van Buren (Left) and Adair County Park (Right) .......................................................................................................... 31 Figure 17: 5 Minute Exposures of Big Dipper Taken at Library Quad (Top) and Adair County Park (Bottom) ....................................................................................................... 33 Figure 18: Ring Nebula Photographed from Valley Library Quad (Left) and Adair County Park (Right) .......................................................................................................... 34 Figure 19: 5 Minute Exposures of Big Dipper Taken From Riverfront Park (Top) and Warm Springs (Bottom) .................................................................................................... 36 Figure 20: Ring Nebula Photographed from Riverfront Park (Left) and Adair County Park (Right) ....................................................................................................................... 37 1. INTRODUCTION Associated with poorly designed or improperly aimed outdoor lighting in urban areas, light pollution has gone from a local nuisance to a global problem in the one hundred years since the advent of the electric light bulb (Ploetz, 2002). As the nighttime glow of cities and suburban areas has increased, the nearly 7000 stars once visible to the naked eye under pristine conditions has shrunk to approximately 25 of the brightest celestial objects in the most light polluted