This image of the Cas A supernova remnant was created with one of the most useful tools in astrophysics— spectrographic analysis. The image shows a typical spectrum from Cas A at each wavelength of x-ray emission. Intensity appears on the vertical axis (the higher the more intense) and wavelength, measured in units of energy, on the horizontal axis (the shorter the wavelength the greater the energy). The “bumps” in this spectrum indicate that at certain wavelengths the radiation is particularly intense. Each bump is associated with the x-ray emission of a particular element under particular physical conditions. These bumps tell astronomers that the elements present are (from left to right): sufur, argon, calcium, and