The eastern & western elongations of Venus, 2007-'17. I. The sunlit hemisphere

Abstract

Fourteen successive morning and evening elongations of Venus from 2007-2017 are reviewed. The work of 153 observers covered the time period of ESA's Venus Express and Japan's Akatsuki missions, and wavelengths from 335-1750nm. The instantaneous rotation period of the ultraviolet markings was studied as a function of latitude, and the results compared with previous wind profile data. We find that the equatorial markings showed the shortest periods (and fastest velocities) with respect to the surface. A small north-south hemispherical inequality in the latitudinal variation of period and velocity is suggested. Comparison of eastern and western elongation data indicates an acceleration of equatorial markings during the Venusian day, from a morning average of -97m/s to -117m/s in the afternoon. Instantaneous measurements of 700-720nm red images yield an average rotation period of 4.72d, considerably longer than the ultraviolet 4d period.