thumb|this image shows an arcuate ridge in terra meridiani. sinus meridiani is a feature name for an albedo feature on mars stretching east-west just south of that planet's equator. it was named by the french astronomer camille flammarion in the late 1870s. it has a diameter of 1622&nbsp;km, and its center is located at 7.12 s and 4 e.http://planetarynames.wr.usgs.gov/searchresults?target=mars&featuretype=terra%2c%20terrae ==observational history== the name sinus meridiani was given to the a classic albedo feature on mars by the french astronomer camille flammarion in the late 1870s. prior astronomers, notably the german team of wilhelm beer and johann heinrich mÃ¤dler and then the italian giovanni schiaparelli, had chosen a particular point on mars as being the location of its prime meridian when they charted their observations. accepting suggestions that dark areas on the surface of mars were seas or oceans, flammarion named a dark area at that point "sinus meridiani", literally "meridian bay", when he worked on his compilation and analysis of all prior observations of mars. since flyby and orbital spacecraft imagery of mars began to become available in the 1960s, dark-light albedo features on the planet have seen shifting of names to reflect the true nature of the topography, and sinus meridiani consequently was given a new designation, terra meridiani ("meridian land"). . however, the older and the newer designations are both in current use. the u.s. geological survey considers the "sinus meridiani" nomenclature canonical united states geological survey, gazetteer of planetary nomenclature; accessed my 21, 2007 ==meridiani planum== the name meridiani planum ("meridian plain") is used to refer specifically to the landing site of mars exploration rover opportunity, in the western portion of sinus meridiani. this site was chosen by the mars exploration rover team both for its characteristic as a flat and mostly rock-free plain (and hence a safe landing site), and also as a site which showed the spectral signature of the mineral hematite, which is often a sign of deposition in an aqueous environment. ==what opportunity rover discovered about rocks and minerals at meridiani planum== thumb|left|the rock "berry bowl". thumb|this image, taken by the microscopic imager, reveals shiny, spherical objects embedded within the trench wall thumb|"blueberries" (hematite spheres) on a rocky outcrop at eagle crater. note the merged triplet in the upper left. opportunity rover found that the soil at meridiani planum was ve
Albedo_features_on_Mars Terrae_on_Mars