Abstract :
Pulsars are celestial objects that emit brief, intense bursts of energy, principally, but not exclusively, at radio frequencies. Several pulsars ``tick´´ at time intervals whose precision exceeds that of quartz crystal clocks and approaches that of atomic time standards. The announcement of the discovery of the first four pulsars, early in 1968, triggered an unparalleled competitive frenzy among radio astronomers to find additional pulsars. By last fall, some 100 of these precisely periodic radio sources had been discovered, theories about what they might be had proliferated and been laid to rest almost as rapidly, and many important new facts about several of them had been elucidated.
