STS-56 Earth observation taken aboard Discovery, Orbiter Vehicle (OV) 103, is of the Strait of Gibraltar. A small bank of clouds marks the passage between Spain and Morocco at the western edge of the Mediterranean Sea. This passage, one of the two Pilars of Hercules of the Ancient Greeks, is now known as the Strait of Gibraltar. The cities of Cadiz on the Atlantic Coast of Spain and Malaga on the Mediterranean coast, as well as Tangier, Morocco (facing the strait), can be seen. According to NASA scientists studying the STS-56 photos, a subtle difference in the water color on the Atlantic side suggests that a pulse of surface water had recently flowed out of the Mediterranean into the Atlantic.