In astronomer detects mysterious pulses in the light from a star at the center of the Crab Nebula, and theorists speculate that the source is a rotating neutron star (a “pulsar”). Massive aluminum cylinders in Illinois and Maryland are suddenly and simultaneously set into vibration, and theorists suggest that a gravitational wave has just passed through the solar system. Radio astronomers discover that space is filled with blackbody radiation at a temperature of about 3 K, and theorists say that it is a by‐product of the initial “big bang” of the Universe. X‐ray astronomers discover aperiodic fluctuations in the x‐ray emission from Cygnus‐X1; optical astronomers discovered that Cygnus‐X1 is associated with a single‐line spectroscopic binary star: from this evidence theorists speculate that the x rays come from a black hole orbit around a normal star.