Gibbous Moon - Several smooth and dark patches on the Moon appear in this photo of the Moon in its gibbous phase. These are the lunar Maria or "seas". These are not actual seas with water (but that's what people once thought), however they are areas where molten rock from underneath the moon's surface has spread and cooled above craters to create these relatively featureless surfaces. Some of the seas visible are the two large Maria: Mare Tranquillitatis (below) and Mare Serenitatis (above). Mare Tranquillitatis or "Sea of Tranquillity" is where the Apollo 11 astronauts landed and set foot on the Moon for the first time in human history.