The persistence and size of thermal anomalies on Venus

During the 1973 to 1974 opportunity, we obtained thermal maps of Venus on 16 days during a span of 43 days just before inferior conjunction. The spatial resolution was about 3 arcsec. The average limb darkening differs from that given by Ingersoll and Orton (1974). Real day-to-day changes in limb darkening were found. An indication of 4-day repetition of a thermal anomaly was found on one occasion. The lifetime of this disturbance probably lies between 4 and 8 days. Solar-related anomalies appear to repeat in most of the images. A southern hemisphere, solar-related disturbance showed significant changes in both position and intensity over 30 days, and we tentatively identify its lifetime as about equal to this period.