Moon rising over Earth's horizon, composite image. The blue haze of Earth's atmosphere can be seen clearly above the horizon, as can many surface features of the Moon. These features include the Copernicus crater, which lies within a dark plain at the terminator (the frontier between light and dark), and lunar maria, large dark basaltic plains formed by ancient volcanic eruptions. Three of the largest maria (at top) are called (from left to right) Mare Serenitatis (sea of serenity), Mare Tranquillitatis (sea of tranquility) and Mare Foecunditatis (sea of fertility). Unlike Earth, the Moon does not have an atmosphere.