Published online by Cambridge University Press: 12 April 2016
Type I or ionic comet tails on the average make an angle of a few degrees at the nucleus with the prolonged radius vector in the direction opposite to the comet’s orbital motion. This fact was explained by Biermann (1951) as the aberration angle caused by the comet’s motion in the outflowing solar wind plasma, and, as is well known, led to the discovery of the solar wind itself.