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Alpha RegioThe first feature identified on Venus using Earth-based radar (it was discovered in 1963). It is a highland plateau about 1300 km across situated in the southern hemisphere of the planet (centered on the Venusian coordinates 25° S latitude, 4° E longitude). It exhibits multiple sets of intersecting ridges, troughs, and flat-floored fault valleys that together form a polygonal outline. Directly south of the complex ridged terrain is a large oval-shaped feature named Eve. A radar bright spot within Eve marks the location of the prime meridian of Venus.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006