THE STRUCTURAL FEATURES OF THE PLANETARY NEBULAE Open PDF Document Details Document Type Technical Report Publication Date Jul 01, 1953 Accession Number AD0020933 Entities People Lawrence H. Aller Organizations Michigan State University Tags DTIC Thesaurus Topics Brightness Calibration Electronic Equipment Elements Emission Excitation High Temperature Hydrogen Images Intensity Machines Observation Observatories Observers Radiation Spatial Distribution Spectra