The average longitudinal motion of a sunspot is shown to be a function of its size and shape. Large groups move up to 2 per cent less rapidly than small groups. Groups that are more or less circular in shape move 1.5-2.0 per cent less rapidly than groups that have longitudinal dimensions many times larger than their latitudinal extent. The usually accepted solar-rotation rate was derived from recurrent spots, which are found predominantly in large circular groups. This rate, therefore, is biased on the low side. A new solar-rotation rate computed from an unbiased selection of spot groups is 1 per cent higher than that calculated by Newton and Nunn, about 0?15 per day. Upward adjustment of the rate brings it into more accord with the rate obtained from motions of faculae and flocculi and produces no more discord with spectroscopic measurements.
No takes yet. Share an insight, caveat, or question.
Fred Ward (1966) studied this question.