Number 100 (Story #4), October 23, 1992 by Phillip F. Schewe and Ben Stein THE OPACITY OF MATTER under conditions like those in stellar interiors has been measured using Livermore's powerful Nova laser (L.B. Da Silva et al, Phys. Rev. Lett., 20 July 1992). The measurements of the photoabsorption of iron, heated by x rays to a temperature of 2.5 x 10**5 K, are in agreement with recent theoretical estimates made at Livermore (the so-called OPAL model) and disagree with an earlier model derived at Los Alamos. Many astronomers had already been rooting for the OPAL model since it had done a better job in predicting certain stellar features, such as the pulsation rate for Cepheids. (Nature, 15 October 1992.)