Cometary brightness variation and nucleus structure

The Bobrovnikoff and Beyer photometric data for more than 100 comets analyzed for intrinsic brightness variations, before and after perihelion, according to some inverse power law of solar distance. The Oort and Schmidt classification of comet age is extended and applied with Marsden's new determinations of inverse semimajor axis. A physical interpretation of the data involves the quick loss of a frosting of supervolatile materials from new comets, and for all comets, the development of an insulating crust after perihelion. The orientation of the axes of rotating comets is shown to be an important factor in cometary brightness variations. A speculation is made concerning the axis of rotation of Comet Kohoutek.