image credit: Ken Cole; larger image

Corner mirror

-- This bicycle reflector is a single piece of cast red plastic containing three sets of corner cubes, each with three flat faces meeting at right angles.  We are seeing it from behind, in transmitted light.  
-- These cubes reflect light back in the direction it came from, in essentially the same way as the corner mirrors that American and Russian astronauts left on the moon in the 1960s and 1970s (see From Physics Research).
-- For a different use of the corner mirror, see the Museum of Modern Art's Corner Mirror and Coral.

(This feature was updated on August 10, 2013.)

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Corner Reflector

For an experiment that shows how a corner mirror works, try the Exploratorium activity Corner Reflector. To understand how light reflects in a corner mirror, check out this page from The Physics Classroom.

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image credit: NASA/Apollo 11; image source; larger image

What Neil and Buzz Left on the Moon

-- Here is part of the one Apollo experiment still functioning--the array of 100 corner mirrors that Apollo 11 astronauts placed on the moon in July of 1969 to reflect laser pulses from Earth back to Earth.  
-- Monitoring these pulses makes possible the precise measurement of the distance to the Moon, as described in What Neil and Buzz Left on the Moon.  
-- To learn more about these corner mirrors, see the Lunar and Planetary Institute's Laser Ranging Reflector and, from the University of California, San Diego, Lunar Reflectors.

The Basics of Lunar Ranging

A project is underway to measure the Earth-moon distance to within 1 mm. To find out how this is done, visit The Basics of Lunar Ranging, and for more information, visit Apache Point Observatory Lunar Laser-ranging Operation.