to identify the egg-shaped nebulosity as a supernova remnant. 
    Not until the advent of x-ray astronomy did Puppis A really earn a place in textbooks. The Einstein Observatory observed the object with both a high-resolution imager and a spectrometer. The observa- tions showed the complexity of the interaction between the supernova and the interstellar medium: a complexity never seen before on such a scale. The observations made with the imager confirmed the prevailing model of the interstellar medium: clouds of all sizes embedded in a hot, low-density gas. Spectroscopic techniques also showed, somewhat unexpectedly, several solar masses of heavier elements such as oxygen and neon.