Today, a look back at the moon landing. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
More than twenty years ago
-- on July 20th, 1969 -- astronauts rabbit-hopped
across the lunar surface and hit golf balls for the
TV cameras. But even then, the bloom was somehow
off the rose. The bread and circuses atmosphere was
wearing thin. The American public was losing
Before they started home, the astronauts quietly
installed an 18-inch, low-tech reflector. It got
little if any press. It was set there to help
measure the quarter-million-mile distance from
earth to the moon. In 1969 we knew the distance
within a mile. That was close enough for space
navigatation, but NASA had other things in mind.
For example, a better knowledge of the distance
would let us check Einstein's general relativity
The reflector made laser ranging possible. By
bouncing a laser pulse off that little target, we
could measure the distance within a few feet. Of
course, astronomers had to hit the reflector from a
quarter million miles away. It was some help that
even a laser beam spreads out in such a long
journey. It's a mile wide when it reaches the
reflector. But that's still like using a rifle to
hit a dime from a distance of two miles. Then they
had to catch the reflected beam when it came back.
By now, more reflectors have been set, and the
measurement has been refined. Today we measure the
distance to the moon within only one inch! That's
astonishing accuracy -- 7 billionths of a percent.
It's like measuring the distance from New York to
Los Angeles within a 50th of an inch.
We've learned a lot from all this. For one thing,
Einstein's general relativity theory is on better
footing. For another, we've learned about changes
in the diameter of the not-quite-solid moon and
earth. The most startling result is that the moon
is drifting away from us. It moves 2½ inches
farther from earth each year.
Meanwhile, these passive reflectors go on serving
us. They don't wear out. The worst that can happen
is that moon dust might cloud their surfaces, but
the lunar surface is so silent that there's been no
sign of that in 20 years of use.
So the astronauts went home, and the circus folded
up. Public interest faded, and funding faded with
it. Yet this modest little reflector reminds us
that the real payoff of all that whoop-de-do was
more interesting than bread and circuses -- more
exciting. Human knowledge has expanded out of sight
of the television cameras, and we've grown as an
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds