Venus: Atmospheric rotation

Photographs of Venus taken in ultraviolet light from September 29, 1963 to May 29, 1971 indicate a general planet-wide circulation in the upper atmosphere of that planet having velocities which varied with time from -87 to -127 m/sec at the equator. Positional measurements on 67 pairs of photographs which show the recurrence of similar patterns after intervals of one to three rotations suggest an asymmetric bimodal distribution of these velocities, with a primary peak at -110.2 ± 0.3 m/sec and a secondary peak at -97.2 ± 0.5 m/sec. These peak velocities correspond to sidereal rotation periods of 4.05 ± 0.01 and 4.59 ± 0.02 days retrograde. The ultraviolet markings appear to be randomly distributed and quite ephemeral in nature, rarely enduring in a recognizable pattern for more than 20 days and usually much less. Attention is directed to an apparent but fictitious mean sidereal rotation period of approximately 4.06 days (3.99 days synodic) derived from observations which are made at a single station and span many months or years. Under such conditions this fictitious value for the rotation period is produced by the commensurability of the 1-day period of Earth and the assumed 4-day period of the atmosphere of Venus.