These radar images show an identical area on Venus (centered at 110 degrees longitude and 64 degrees north latitude) as imaged by the U.S. Magellan spacecraft in 1991 (left) and the U.S.S.R. Venera 15/16 spacecraft in the early 1980's (right).  Illumination is from the left (or west) in the Magellan image (left) and from the right (or east) in the Venera image (right).  Differences in apparent shading in the images are due to differences in the two radar imaging systems.  Prior to Magellan, the Venera 15/16 data was the best available for scientists studying Venus.  Much greater detail is visible in the Magellan image owing to the greater resolution of the Magellan radar system.  In the area seen here, approximately 200 small volcanoes, ranging in diameter from 2 to 12 kilometers (1.2 to 7.4 miles) can be identified.  These volcanoes were first identified as small hills in Venera 15/16 images and were predicted to be shield-type volcanoes constructed mainly from eruptions of fluid lava flows similar to those that produce the Hawaiian Islands and sea floor volcanoes -- a prediction that was confirmed by Magellan.  These small shield-type volcanoes are the most abundant geologic feature on the surface of Venus, believed to number in the hundreds of thousands, perhaps millions, and are important evidence in understanding the geologic evolution of the planet.  The only other planet in our Solar System with this large number of volcanoes is Earth.  Clearly visible in the Magellan image are details of volcano morphology, such as variation in slope, the occurrence and size range of summit craters, and geologic age relationships between adjacent volcanoes, as well as additional volcanoes that were not identifiable in the Venera image.