The term 'SEA of Tranquility' is a reference to the SEA of Tranquility, a large, dark, flat area on the moon. It was the site of the first human landing on the moon, when Apollo 11 astronauts Neil Armstrong and Edwin 'BUZZ' Aldrin became the first humans to walk on the moon in 1969. The SEA of Tranquility is located in the northern hemisphere of the moon and is one of the most recognizable features of the lunar surface.