The Moon is Earth’s closest companion in the night sky. The Moon has been an important part of scientific study and human culture throughout human history. Thanks to modern technology, more is known about the Moon today than ever before. At this time a total of 13 countries have sent robotic missions to the Moon, including the Soviet Union, the United States, Japan, the European Space Agency, China, India, Luxembourg, Israel, Italy, South Korea, the United Arab Emirates, Russia, Mexico, and Pakistan.
During the early formation of the solar system, the Moon was formed when the protoplanet Earth was impacted by another smaller protoplanet, known today as Theia. The debris that was blasted away from the surface of Earth by the impact then clumped together to form the Moon. Scientists know this because the samples of Moon rocks that were returned to Earth from the Apollo missions are made of the same minerals as Earth’s crust. Today, some scientists believe that remnants of the impactor Theia have been identified under Earth’s crust near the core.
The close proximity of the Moon to the Earth means that the gravity of the Moon is felt here on Earth. The gravity of the Moon pulls on the water in all of the oceans on Earth, causing the rise and fall of the tides. The Earth in turn pulls on the Moon. Over the lifetime of the Earth/Moon system, the gravity of the Earth has slowed the rotation of the Moon until the same side of the Moon always faces the Earth. This arrangement is the most stable orbit for the Moon and is known as “tidal locking.” The tidal forces between the Earth and the Moon have locked the Moon to always show the same face to the Earth.
The United States is the only country to successfully send humans to explore the surface of the Moon and return them safely to Earth. These were the Apollo Moon missions. In 1962, President John F. Kennedy announced a mission for the United States to send astronauts to the Moon before 1970. After years of technology development, NASA sent Apollo 11 to be the first manned mission to land on the Moon in July, 1969. On July 20, 1969, Neil Armstrong was the first human to walk on another world, followed shortly by his companion astronaut Buzz Aldrin. Between the years 1969 and 1972 NASA sent nine manned missions to the Moon. Across all nine missions, the Apollo astronauts returned 842 pounds of Moon rocks, most of which are stored at the NASA facility in Houston, Texas.
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