Mt. Wilson Observatory astronomers Robert Howard and Barry J. LaBonte have correlated currents of east-west motion on the sun's surface with the rhythm of the 11-year sunspot cycle and the regions of heaviest sunspot activity.
The researchers analyzed 12 years of digital full-disk data on the 5250-Å line of Fe I. These were recorded daily with the magnetograph of the 45.72-m tower telescope at Mt. Wilson. Velocities were determined from wavelength shifts, and after compensating for the varying rates of rotation at different latitudes, the astronomers found what they describe as alternating zones of slow and fast rotation. The bands of rapid motion averaged 3 m/s faster than the average speed of rotation at any given latitude; slow bands averaged a similar amount less than the average velocity. (At the poles, the sun rotates once every 33 days; at the equator, once every 25 days.