Composite Analytical Photography of Polarized Objects

F. Zwicky
1956 Publications of the Astronomical Society of the Pacific  
One of the first applications of composite photography for color was made by Fehrenbach and Daudin in their search for red stars. 1 Later Gum used this method to map nebulosities with Ha emission. 2 In some recent articles I proposed a general method of using black and white photography to analyze one by one all of the properties of light emanating from various objects. 3 My efforts were directed at first toward the analysis of differently colored stellar populations within galaxies of various
more » ... tructural types, and some rather striking results were obtained. 4 As a second step in the exploitation of composite photography I present here the application of this method to the analysis of polarized objects. Consider the simple case of a celestial field photographed, first, on a plate mounted behind a polaroid filter transmitting only light polarized in the direction designated as I and, second, on a plate with the same emulsion and exposure time behind a polaroid filter transmitting only light polarized in the direction II, at right angles to I. Let the photographic negative and positive be denoted by the upper indices (") and ( + ), respectively. When I" is superposed on IL and the resulting composite is viewed as a transparent, the following features appear on (I ' II+) - 1. Stars whose light is partly or fully polarized in the direction I will produce black spots. Stars whose light is polarized in the direction II will appear as black spots with white (transparent) rings around them. The rings become full disks if the polarization is complete along II. On composites (I + II') conditions are reversed. 2. Surfaces whose light is partly or fully polarized along the direction I will appear darker than unpolarized areas such as the general sky background, for instance. On the other hand, surfaces 121
doi:10.1086/126894 fatcat:r5jy4ugj7zf6po3wmsmmbf2qcy