The Moon is Earth's only natural satellite and is the fifth largest satellite in the Solar System. It is the largest natural satellite in the Solar System relative to the size of its planet, a quarter the diameter of Earth and 1/81 its mass, and is the second densest satellite after Io. It is in synchronous rotation with Earth, always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal. Its prominence in the sky and its regular cycle of phases have since ancient times made the Moon an important cultural influence on language, the calendar, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to be the same size in the sky as the Sun—allowing the Moon to cover the Sun precisely in total solar eclipses.
The Apollo 11 space flight landed the first humans on Earth's Moon on July 20, 1969. The mission, carried out by the United States, is considered a major accomplishment in the history of exploration and represented a victory by the U.S. in the Cold WarSpace Race with the Soviet Union. Launched from Florida on July 16, the third lunar mission of NASA's Apollo program (and the only G-type mission) was crewed by Commander Neil Alden Armstrong, Command Module Pilot Michael Collins, and Lunar Module Pilot Edwin Eugene "Buzz" Aldrin, Jr. On July 20, Armstrong and Aldrin landed in the Sea of Tranquility and became the first humans to walk on the Moon. Their landing craft, Eagle, spent 21 hours and 31 minutes on the lunar surface while Collins orbited above in the command ship, Columbia. The three astronauts returned to Earth with 47.5 pounds (21.55 kilograms) of lunar rocks and landed in the Pacific Ocean on July 24. Apollo 11 fulfilled U.S. President John F. Kennedy's goal of reaching the moon before the Soviet Union by the end of the 1960s, which he had expressed during a 1961 mission statement before the United States Congress: "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth."
A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra (shadow). This can occur only when the Sun, Earth, and Moon are aligned (in "syzygy") exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a full moon. The type and length of an eclipse depend upon the Moon's location relative to its orbital nodes.