Split Personality

The names bestowed on the Moon's dark features almost seem to give it a split personality. Most of the names on the right side (the eastern hemisphere) have calm connotations, while those on the left (the western hemisphere) have stormier connotations. Although they are named for seas or oceans, all of these features are vast plains of volcanic rock that formed about four billion years ago. [NASA/GSFC/Arizona State University]