The Sun's Rotation Derived from Sunspots 1934-1944 and Additional Results

Results are given for the Sun's daily sidereal motion ( ξ ) derived from 136 single recurrent sunspots for the cycle 1934–1944. The expression relating ξ to solar latitude ( ϕ ) so derived, $$\xi\,14^{\circ} .38-2^{\circ} .96\,\text{sin}^{2}\,\phi$$ , is in satisfactory accordance with values from similar data for the five previous 11-year cycles. A good internal- accordance of measures is found by comparing ξ values derived from a full rotation period interval (27 days) with the mean ( ξ₁ ), given by the two separate disk-passages of the same spot. From the combined data of six sunspot cycles there appears no measurable variation in the Sun's rotation period (1) with alternate 11-year cycles, (2) within the (mean) cycle itself. Neither do the two hemispheres, north and south, behave differently. Although not included in the discussion, the derived expression for the daily sidereal motion from non-recurrent spots, 1934–1944, is stated as a point of interest in the Addendum.