Before humans walked on the moon...
We crashed landed some probes onto the moon (starting with the U.S.S.R.'s Luna 3 in 1959, and we also bounced a laser beam off of the moon!
On this date in 1962, MIT scientists bounced laser light—a series of high-intensity red flashes—off of the surface of the moon, and then detected the reflections back here on Earth. It was the first time that a laser beam had crossed space.
Nowadays we can can aim our lasers at the retroreflectors Apollo astronauts positioned on the moon. This is an amazing feat, because the reflectors are so small compared to the distance crossed, and of course the moon is always in motion, orbiting around the Earth; the accuracy of hitting the reflectors is like using a rifle to hit a moving dime two miles away! By measuring the time it takes the reflected light to return to Earth, we can measure the distance from the Earth to the moon.
And we can measure this very large distance incredibly accurately! It's like measuring the distance between Los Angeles and New York to one hundredth of an inch.
We have discovered that the moon is spiraling away from the Earth at a rate of 38 millimeters per year. Granted, this isn't an incredibly fast retreat—but some scientists say that it is faster than expected.
The very precise, multiple measurements of the moon's distance have been used as evidence that Einstein's general theory of relativity is correct, as the theory predicts the lunar orbit discovered through these measurements. Also, the presence of the reflectors has been used as evidence that humans actually went to the moon. You wouldn't think anybody would need to build a case that people went to the moon—everybody knows about the Apollo program and the moon rocks and the “one giant leap for mankind,” right?—but some people have claimed that the moon landings were faked! There was even a television show—supposedly non-fiction—that claimed to prove that American astronauts never went to the moon. (Let that be proof that you really, really, really can't believe everything you see on TV—not even the news or “documentaries.”) Check out this website that debunks the bad science in the moon-landing conspiracy theories.
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