Part 1 of Essay
A is a STAR that explodes. It suddenly increases in brightness by a factor of many billions, and within a few weeks it slowly fades. In terms of the human lifespan, such explosions are rare occurrences. In our Milky Way galaxy, for example, a may be observed every few hundred years. Three such explosions are recorded in ....

Part 2 of Essay
.... few days than the Sun does in 100 million years, and the energy expended in ejecting material is much greater even than this. In many cases, including the Crab nebula supernova, the stellar remnant left behind after the explosion is a NEUTRON STAR--a star only a few kilometers in diameter having an enormously large density and consisting mainly of neutrons--or a PULSAR, a pulsating neutron star. There are two common types of supernovas, called type I and type II. Type I occurs among old stars of small mass, ....