The cometary nucleus: Current concepts

Ideas concerning the nature of cometary nuclei as modified by observations of recent years, particularly by those of Halley's comet during the 1986 apparition are reviewed. The major trend is to increase the postulated dimensions of the nuclei and reduce their albedos. The Vega and Giotto missions establish an invaluable checkpoint with regard to comet nuclei. These and other observations are affecting opinions concerning many facets of cometary nature, origin, evolution, and decay.