The Institute - December 2019 - 15

tech history

One Apollo 11 Experiment
Is Still Going 50 Years Later
It gave NASA the ability to precisely measure
the distance between the Earth and the moon

TOM ZAGWODZKI/GODDARD SPACE FLIGHT CENTER

IF NOTHING ELSE will

convince someone
that humans once walked
on the moon, NASA's lunar
ranging experiment (LURE)
should. It's because of that
experiment that scientists
know the precise distance
between the Earth and the
moon with centimeter
accuracy.
The LURE's first demonstration began on 1 August
1969, when a pulse of trillions of photons was shot
out of a telescope at the
Lick Observatory on Mount
Hamilton, outside of San
Jose, Calif. The laser pulse
traveled to the moon and
returned after reflecting off
a 1-meter-wide array of mirrors-retroreflectors-that
Apollo 11 astronauts had
placed on the lunar surface
12 days earlier.
The Apollo 11 LURE was
dedicated as an IEEE Milestone at the Lick Observatory on the 50th anniversary
Lunar laser ranging is still done today including at
of the experiment's first sucGoddard's Laser Ranging Facility in Greenbelt, Md.
cess. The IEEE Santa Clara
Pictured is the technology directing a laser toward
(California) Valley Section
a spacecraft in orbit around the moon in 2009.
sponsored the Milestone.
In the five years that followed that 1969 experiment,
other missions, such as Apollo 14 and 15
The information collected from the
in 1971, placed additional mirror arrays experiment has allowed researchon the surface.
ers to better understand changes in
The arrays have shown that the dis- Earth's rotation and has improved
tance to the moon increases by nearly their knowledge about continental
4 centimeters per year.
drift. It also has provided additional

evidence supporting Albert Einstein's
general theory of relativity, which
accounts for gravity.
Lunar laser ranging is still performed
routinely today to track the moon's orbit
and variations in its rotation.
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https://www.nasa.gov/ https://www.ucolick.org/main/visit/info.html http://ieeemilestones.ethw.org/milestone-proposal:apollo_11_lunar_ranging_experiment_(lure http://ieeemilestones.ethw.org/milestone-proposal:apollo_11_lunar_ranging_experiment_(lure http://sites.ieee.org/scv/ http://sites.ieee.org/scv/ http://www.discovermagazine.com/2019/may/how-to-understand-einsteins-theory-of-gravity http://www.discovermagazine.com/2019/may/how-to-understand-einsteins-theory-of-gravity

The Institute - December 2019

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