X Rays From the Rest of the Universe Available to Purchase

Just as x rays from a cathode‐ray tube in Wilhelm Röntgen's laboratory revealed the bones in his wife's hand, x rays from space have revealed new objects and physical processes hidden from the view of optical telescopes. X rays from beyond Earth's atmosphere were first detected in 1949 in a 5‐minute V‐2 rocket observation of the Sun. Thirteen years later, the first nocturnal rocket flight quite unexpectedly discovered the existence of a diffuse isotropic glow of 10‐kilo‐electron‐volt x rays across the celestial sphere, as well as the first discrete source of x‐ray emission from beyond the Solar System. By 1965 the number of known sources of celestial x rays totaled 10; at this writing the number exceeds $105.$