THE CRAB NEBULA

A whole treatise on the Crab Nebula? Well, Simon Mitton, Secretary of the Institute of Astronomy at Cambridge, goes far in convincing us that his favorite may indeed be the most fascinating object in the observable universe. The Crab Nebula, he explains, is the remnant of a huge supernova explosion which took place in 1054 A.D. Thoroughly recorded by Chinese observers, it was apparently ignored in the West. (Mitton suggests that the Dark Ages or Aristotelian prejudices might have made us untuneful to anomalies in the supposedly changeless heavens.) With the dawn and flowering of modern astronomy, it now appears that at the heart of the nebula lies an invisible neutron star, only kilometers across, whose spinning establishes the rapid pulse of a ""pulsar""--flashes observable at frequencies throughout the electromagnetic spectrum. Moreover, ""synchroton"" processes in the nebula--the behavior of very fast electrons in a magnetic field--provide the power for the pulsar's emissions. As Mitton suggests in his last chapter, the behavior of the Crab Nebula may be a microcosm of the vast energy processes required to power emissions from radio galaxies and quasars. Not the least of Mitton's contagious excitement and enthusiasm comes from his accounts of discoveries. The four astronomers who first picked up the 30-times-a-second pulsar flashes had all but abandoned hope at Kitt Peak when word came that the astronomer next in line to use the telescope could not come because Iris wife was ill. They made a last minute check of their calculations and discovered a wrong sign in an equation; the rest, as they say, was history. Neatly told, but what with some heavy emphasis on energy budgets, theories, and the like, not for the novice.