homehome Home chatchat Notifications


What Neil Armstrong and Buzz Aldrin left behind

Perhaps the most famous thing left behind on the Moon is a footprint, a boot-shaped impression in the moon dust, photographed and viewed by millions of people. If everything goes according to plan, in the future, many people visiting the Moon will look at it and refer to it as ‘the first’. But about 100 […]

Mihai Andrei
February 16, 2012 @ 10:46 am

share Share

Perhaps the most famous thing left behind on the Moon is a footprint, a boot-shaped impression in the moon dust, photographed and viewed by millions of people. If everything goes according to plan, in the future, many people visiting the Moon will look at it and refer to it as ‘the first’. But about 100 feet away, in the Sea of Tranquility, Armstrong left something more important, forgotten by most.

The Sea of Tranquility is a huge basaltic plain on the Moon, where the first human mission ever landed on the Moon. There, next to the famous footprint, still lies a 2-foot wide panel studded with 100 mirrors pointing at Earth: the “lunar laser ranging retroreflector array”. Armstrong and Aldrin put it there on July 21, 1969, less than an hour before their last moonwalk (no Michael Jackson jokes, please). Now, thirty-five years later, it is the only Apollo scientific experiment still functioning.

Here’s how it works, basically: a laser pulse shoots out of a telescope on Earth, travels the distance to the satellite and this the array. Because the mirrors are “corner-cube reflectors”, they send the pulse exactly where it came from, pretty much like hitting a squash ball in the corner of the room. Back on Earth, the pulse is recaptured, even though it usually consists of a single photon, thus giving an incredibly accurate estimate of the Earth-Moon distance, which is usually just a few cm bigger than 385,000 km.

Of course, targeting the mirrors and then recapturing the pulse is a tricky business, but astronomers have been successfully doing it for the past 35 years, and in this way, the Moon’s orbit was more accurately calculated. But even more interestingly, we’ve found out more things about the satellite this way:

  • The Moon is spiraling away from the Earth at a rate of 3.8 cm per year
  • The Moon has a liquid core
  • The Universal force of gravity is really stable. Newton’s gravitational constant G has changed less than 1 part in 100-billion since the laser experiments began.

Physicists have also used this array to test Einstein’s theory of relativity, since before particle accelerators were a big thing, and so far, so good. All in all, just one piece of simple device, a mirror array, helped us learn so much, we just have to pay tribute to it, and the people who thought of applying this system.

share Share

A Rocket Carried Cannabis Seeds and 166 Human Remains into Space But Their Capsule Never Made It Back

The spacecraft crashed into the Pacific Ocean after a parachute failure, ending a bold experiment in space biology and memorial spaceflight.

An Asteroid Might Hit the Moon in 2032 and Turn It Into a Massive Fireworks Show from Earth

The next big space threat isn't to Earth. It's to the Moon.

This Colorful Galaxy Map Is So Detailed You Can See Stars Being Born

Astronomers unveil the most detailed portrait yet of a nearby spiral galaxy’s complex inner life

A NASA Spacecraft Just Spotted a Volcano on Mars Like We Have Never Seen Before

NASA's Mars Odyssey captures a surreal new image of Arsia Mons at sunrise

Astronomers Found a Volcano Hiding in Plain Sight on Mars

It's not active now, and it hasn't been active for some time, but it's a volcano.

The World’s Largest Camera Is About to Change Astronomy Forever

A new telescope camera promises a 10-year, 3.2-billion-pixel journey through the southern sky.

The Sun Will Annihilate Earth in 5 Billion Years But Life Could Move to Jupiter's Icy Moon Europa

When the Sun turns into a Red Giant, Europa could be life's final hope in the solar system.

A Massive Particle Blasted Through Earth and Scientists Think It Might Be The First Detection of Dark Matter

A deep-sea telescope may have just caught dark matter in action for the first time.

Scientists Used Lasers To Finally Explain How Tiny Dunes Form -- And This Might Hold Clues to Other Worlds

Decoding how sand grains move and accumulate on Earth can also help scientists understand dune formation on Mars.

Astronomers Claim the Big Bang May Have Taken Place Inside a Black Hole

Was the “Big Bang” a cosmic rebound? New study suggests the Universe may have started inside a giant black hole.