The Sea of Tranquility is a large, flat area on the surface of the Moon, known for its smooth, dark basalt plains. It is one of the lunar maria, which are ancient volcanic features formed by lava flows. The Sea of Tranquility is located in the Moon's northeastern quadrant and covers about 400,000 square kilometers. This region is historically significant as it was the landing site of the Apollo 11 mission in 1969, where astronauts Neil Armstrong and Buzz Aldrin became the first humans to walk on the Moon. The Sea of Tranquility is often associated with peace and calmness, reflecting its name.