The Crab Nebula (previous
page) is a supernova in our galaxy, the remnants of a particularly
violent stellar explosion that occurred in the summer of 1054 A.D.
Western Europe was too primitive to notice such things then, although
it is surprising that Arabian astronomers missed it. But the Japanese
and the royal astronomers of the Sung Dynasty in China took note
of it. Three such violent supernovae have been observed in our own
galaxy in recorded history, in 1054, 1572, and 1604.
a search for supernovae in other galaxies conducted at the Palomar
Observatory for many years suggests that a typical galaxy might
produce a supernova every thirty years. The Crab Nebula is a hotbed
of turmoil, emitting radio noise and X-rays as well as light, and
having a pulsar at its core. The theoretical astronomer has no trouble
explaining why stars become supernovae; rather the problem is to
explain why such catastrophes are not seen more often.