Form and motion of cometary tails.

This work deals with the geometrical problems inherent in the observation of cometary tails, and with attempts at explanation of their forms. Following the introduction, a review of the geometrical aspects of tail observation is presented in Chapter 2. New formulae are developed for projection from photographic to orbital plane, and for foreshortening etc. Tail orientation is fully treated and expressions are derived for orientation error in this projection. Equations for an elliptic orbit are developed in addition to those for the usual assumption of a parabolic orbit. Perspective error resulting from bisection of apparent tail images is investigated, and appropriate formulae derived. A set of observations of Comet Bennett 1969i is analysed and the results compared with those of other workers. The influence of the solar wind on Type I tails is reviewed in Chapter 3 with special reference to dynamical aberration: some results for Comet Bennett are presented. Oscillation of Type I tails is then discussed. A comparison made between the cases of Comet Burnham 1960 II and Comet Halley 1835 III lends some support to the view that the oscillations are due to external influences on the tail. Formulae are developed for the progressive change in Type I tail orientation to be expected as the comet pursues its orbit. Mechanical theories of Type II tails are reviewed in Chapter 4, special attention being given to tail orientation. The accurate calculation of syndyne and synchrone curves is treated, and the formulae are extended to allow of any value of 1-4. Tail analysis by syndynes and synchrones is considered; results are presented for the time variation in the initial orientation of these curves. Implications for mixed tails and possible coupling between tails are discussed. Finally, Chapter 5 briefly summarises the conclusions and gives suggestions for further work.