Constructing a spectral photometer for the study of light pollution

Abstract

In this paper, I describe a method and apparatus for carrying out a systematic spectroscopic mapping I([lambda], z, [Phi]) of the night sky, as proposed by Stefano Rosoni. Once completed, this method should prove to be simple and effective, while the SLR film camera spectral photometer constructed and described within should prove to be inexpensive and easily reproducible. The spectral photometer is simply a single slit diffraction apparatus mounted to the rear of a telescope. The resulting interference pattern is recorded as an image projected on the film inside the camera. In order to correlate the image recorded on the film to a spectrum containing information about the intensity and wavelength of the light pollution, the photographs were scanned into digital format and analyzed by a series of computer programs. While a film spectral photometer is in itself, nothing new, the computer algorithm used to extrapolate film response curves was developed by Paul Debeveck and Jitendra Malik for use in computer graphics. I apply their algorithm to the problem of calibration of a spectral photometer and bypass the myriad of tedious and time consuming calibrations which make film cameras almost more trouble than they are worth. Problems from the unsuccessful first prototype are discussed, as well as suggested improvements for further versions PACS numbers: 95.45. + i, 95.55.Qf, 95.75.Pq