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Luna See

May 9, 2012

The Moon stands due south at first light tomorrow. The portion that’s illuminated by sunlight includes an area of bright, jumbled terrain known as the southern highlands.

That region was the first target for an experiment that began 50 years ago tonight — an experiment that helped set up a test of Albert Einstein’s theory of gravity that continues today.

The experiment was called Luna See. Scientists and engineers from MIT aimed a red laser at the lunar surface. Over three nights, they fired the laser 80 times, and used a telescope to measure its reflection.

The experiment didn’t provide much scientific return, but it did show that you could bounce a laser off the Moon. And that set up an experiment that’s still running.

Apollo astronauts and unmanned Soviet rovers left special reflectors on the Moon to bounce lasers back to Earth more efficiently than by using the Moon itself. And scientists have been using those reflectors ever since. Among other things, their work has helped probe the Moon’s interior and measured how quickly the Moon is moving away from Earth.

The work has also provided a test of Einstein’s theory of gravity, General Relativity, by measuring the motions of Earth and the Moon around the Sun. So far, the experiment has confirmed Einstein’s equations. But today they’re using bigger telescopes and a more powerful laser to continue the experiment — providing an even better test of General Relativity.

More tomorrow.


Script by Damond Benningfield, Copyright 2012


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