This Apollo 11 experiment is still happening on the moon

When astronauts Neil Armstrong and Buzz Aldrin walked on the surface of the moon 50 years ago, they took photos, collected lunar rock samples and left behind an experiment that’s still sending back data.

Aldrin placed an array – an arrangement of 100 quartz glass prisms in rows – on the surface. Later, the Apollo 14 and 15 missions would also add similar arrays to the surface.

The simple experiment doesn’t require any power, which is why it’s still serving a purpose.

The Apollo 11 array.

The arrays reflect light, which is full of valuable insight, back towards Earth. Observatories in Italy, France, Germany and New Mexico regularly aim lasers at the arrays and note the time it takes for the light to return to Earth, according to NASA.

Scientists can measure that distance down to a few millimeters. This allows researchers to determine the moon’s orbit, rotation and its current orientation, which will be needed to land on the moon. They also act like mile markers for the cameras attached to spacecraft.

Although we know that the moon is about 239,000 miles away, the arrays allowed scientists to determine that this distance actually increases by an inch and a half each year.

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Previously it was believed that the moon had a solid core, but data from the arrays has revealed that the core is fluid. This core determines the direction of the lunar poles, which the array data can also help determine through orientation.

Over the next decade, new and improved reflectors will be placed in different areas on the moon to study more about the moon’s interior, a glimpse into its past and help with future exploration.

Apollo 11 astronaut Edwin "Buzz" Aldrin salutes the American flag on the surface of the moon on July 20, 1969. Aldrin was the second man to ever step foot on the lunar surface. The first was Neil Armstrong, Apollo 11's mission commander.

Apollo 11's crew is pictured in May 1969, the month before the launch. From left are Armstrong, Michael Collins and Aldrin. Collins piloted the command module that orbited the moon while Armstrong and Aldrin spent time on the surface.

Apollo 11 was launched into space by a Saturn V rocket on July 16, 1969.

Former US President Lyndon B. Johnson and then-Vice President Spiro Agnew were among those watching the launch at Florida's Kennedy Space Center.

It took the crew 76 hours to travel 240,000 miles from the Earth to the moon.

The Apollo 11 spacecraft consisted of a command module, Columbia, and a lunar module, Eagle. This photo, taken from the Eagle lunar module, shows the Columbia command module pulling away near the lunar surface.

Armstrong works outside the Eagle module shortly after becoming the first man to step foot on the lunar surface. There aren't that many photos of Armstrong on the moon. That's because he was the one taking most of the photos.

Fans attending a Philadelphia Phillies baseball game cheer after it was announced that the Eagle had made a safe lunar landing on July 20, 1969.

Armstrong is pictured aboard the Eagle just after the historic moonwalk. As Armstrong lowered himself to the surface, people watching around the world heard him call it "one small step for man, one giant leap for mankind." Armstrong later said he had intended to say "a man" and thought he had. Numerous studies have been carried out over the years to discover whether he had indeed uttered that one little sound. Either way, his intention was clear.

A view of Earth appears over the lunar horizon as Apollo 11's command module comes into view of the moon.

Aldrin walks on the surface of the moon. He and Armstrong spent a little over two hours collecting rock samples and data near the moon's Sea of Tranquility region. They also left behind a plaque signed by all three crew members and President Richard Nixon. The plaque reads: "Here men from the planet Earth first set foot upon the moon, July 1969 A.D. We came in peace for all mankind."

Aldrin's family and friends watch the mission from his home in Texas. Aldrin's wife, Joan, is in the polka-dot shirt. ABC, CBS and NBC spent between $11 million and $12 million to cover the mission from July 20-21.

An astronaut's boot print on the lunar surface.

Aldrin co-piloted the Eagle lander to the surface.

A view of Earth, photographed from Apollo 11 as it returned from the moon.

US Navy personnel assist the astronauts after their re-entry vehicle landed safely in the Pacific Ocean on July 24, 1969.

NASA officials and flight controllers celebrate the successful conclusion of the mission.

President Nixon spends time with the astronauts, who were in a quarantine trailer for their first few days back on Earth. From left are Armstrong, Collins and Aldrin. Since Apollo 11, only 10 other men have walked on the moon. The last was in 1972.

The Apollo 11 moon landing, in photos

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In order for NASA to even reach the moon in the first place in 1969, cameras were sent to capture detail about the lunar surface to ensure that the astronauts and anything else touching the moon wouldn’t sink down into the dust.

Until 1964, there weren’t any closeup or detailed photos of the lunar surface.

Cygnus OB2

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NASA’s Ranger spacecraft were designed to orbit the moon and document the surface. The first few either didn’t escape low-Earth orbit or missed the moon entirely. Others were intentionally crashed into the moon but didn’t return any images before impact.

The first image sent back by Ranger 7.

In 1964, Ranger 7 successfully reached the moon and returned 4,316 images of the surface before it collided intentionally with the surface.

The area where it crashed was called Mare Cognitum, which is Latin for “The Sea that has Become Known.” Ranger 8 and Ranger 9 would send back thousands more images and live images of a moon crater, which would enable the next steps of lunar exploration.

NASA has created a goal of landing the first woman and next man on the moon’s South Pole by 2024. NASA has dubbed this path back to the moon Artemis, after Apollo’s twin sister in Greek mythology. The agency also wants to establish a sustained human presence on and around the moon by 2028.