Number 19 (Story #2), January 29, 1991 by Phillip F. Schewe and Ben Stein THE STRUCTURE OF ACTIVE GALACTIC NUCLEI (AGN) have been studied by astronomers using data from the International Ultraviolet Explorer (IUE). Concentrating on the AGN at the heart of the Seyfert galaxy NGC5548, they measured both the continuous-spectrum radiation coming from the primary-energy source (perhaps containing a black hole) and the emission-line (broad, discrete spectral lines) radiation from the clouds of material surrounding the source. The pattern of variability of the two light curves over eight months allowed the astronomers (contact: Julian Krolik, Johns Hopkins, 301-338-7926) to surmise that highly-ionized material (e.g., N (4+)) is distributed rather spherically (at about a radius of 30 light days) around the core, while less-ionized material (e.g., C (2+)) is arranged in a disk or ring at a distance of 20 to 100 light days. (Physics World, December 1990.)