the accompanying diagram identifies the largest 'seas'. Mare Tranquillitatis,the Sea of Tranquility,is famous as the site where Neil Armstrong first set foot in 1969. To its upper left is Mare Serenitatis, the Sea of Serenity, and Mare Imbrium, the Sea of Rains. All three are roughly circular, the result of lava's flooding gigantic craters left by meteorite impacts when the moon was young. To their left is the larger, more formless Oceanus Procellarum, the Ocean of Stroms, with Mare Humorum (Sea of Moisture) and Mare Numbium (Sea of Clouds) below it. The large bright areas are mountainous, cratered terrain made of lighter colored rock. Tiny bright patches in Oceanus Procellarum aree splashes of bright-colored rock kicked up by the formation of individual craters.