It's almost 50 years since the United States became the first country to land men on the moon.
The Apollo 11 mission was a great moment in the United States and world history, but what just happened and why does it matter?
Why did the US want to go to the moon?
A space race developed between the United States and the then Soviet Union after the launch of the first Soviet Sputnik satellite in 1
When John F Kennedy became the United States president in 1961, many Americans believed that they lost race for technological superiority to their cold war figure.
It was in that year that the Soviet Union made the first ever manned space flight.
The United States was determined to get a manned mission here first and in 1962 Kennedy made a famous speech announcing: "We choose to go to the moon!"
The space race continued, and in 1965 the Soviets successfully led an unmanned craft to touch the moon.
How did the US plan the plan for its mission?
The US space company, Nasa, committed itself to huge amounts of resources for what became known as the Apollo program.
About 400,000 people worked on the 17 Apollo missions at $ 25 billion.
Three astronauts were selected for the Apollo 11 mission: Buzz Aldrin, Neil Armstrong and Michael Collins.
A strong rocket – Saturn V – brought the Apollo command and service module and the attached moon module to touch the moon.
The plan was to use the Earth's orbit to reach the Moon, after which Armstrong and Aldrin would enter the Moon module. They were supposed to fall to the surface of the moon, while Collins was back in the command and service module.
Did everything go wrong?
The first crew flight to test in circulation was Apollo 1 in 1967.
But the disaster struck during routine checks before the flight, as fire struck through the command module and killed three astronauts.
Managed space flights were suspended for several months.
During the Apollo 11 mission itself, there were communication problems with ground control. And an alarm message sounded on the computer that the crew had never heard before.
The moon module also ended up moving down from the original target area.
Walking on the Moon
Despite these problems, Neil Armstrong on July 20 – almost 110 hours after leaving the ground – became the first person to step on the Moon's surface. He was followed 20 minutes later by Buzz Aldrin.
Armstrong's words, beamed to the world by television, came into the story: "It's a small step for a man, a big step for mankind."
The two men spent more than two hours outside the moon module, collecting samples from the surface, taking pictures, and creating a number of scientific experiments.
After completing their Moon exploration, the two men have successfully docked with the command and service module.
The return to Earth began and the crew sprayed into the Pacific on July 24.
Estimated 650 million people worldwide had seen the first moon landing. For the United States, the performance contributed to demonstrating its power to a world audience.
It was also an important boost to national self-esteem at the end of a tumultuous decade. It had seen Kennedy murdered, racist in major cities and worried about its military involvement in Vietnam.
How do we know it really happened?
A total of six American missions had landed men on the moon's surface at the end in 1972, but to this day there are conspiracy theories that say the landings were staged.
But Nasa has had a reconnaissance vessel orbiting the moon since 2009. It sends back high-resolution images showing signs of exploration on the surface of Apollo missions, such as footprints and wheel tracks.
There are also geological evidence from rocks brought back from the surface.
What is the purpose of going to the moon?
The United States is the only country that has put people on the Moon's surface.
But Russia, Japan, China, the European Space Agency and India have either sent probes to the Moon or landed vehicles on its surface.
For a country to do so is a sign of its technological skill, giving it membership of an elite club.
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There are also more practical reasons for wanting to exploit its resources.
Ice foundations in both poles can make it easier for craft to reach deeper into space as it contains hydrogen and oxygen that can be used for fuel rockets.
There is also interest in mining the moon for gold, platinum and rare earth metals, although it is not yet clear how easy it would be to extract such resources.
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