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"The Dark Side of the Moon" made a memorable album title for the rock group Pink Floyd in 1973. But the term is a common misnomer. The moon rotates like Earth, but so slowly it keeps one side facing Earth though synchronous rotation. When we have new moon on Earth, the lunar far side is fully illuminated; there is no "dark side."

It may seem hard to believe, but a few decades ago we didn’t have clue as to what the far side of the moon looked like. One cartoon showed it to be the backside of a highway billboard.


 

At the birth of the Space Race in the late 1950s the Soviet Union sent the Luna 3 probe to take the first ever snapshot of an unknown landscape so close to Earth.

To everyone’s surprise the fuzzy photos showed few mare -- circular frozen lava seas -- on the far side, unlike the “face of the man in the moon” near side. In fact there were only two regions, which the Soviets dutifully named Mare Moscovrae (Sea of Moscow) and Mare Desiderii (Sea of Desire). The moon was found to be two-faced.

Now little more the 50 years later we have the lunar far side topographically mapped to an extraordinary level of precision with instruments aboard NASA’s Lunar Reconnaissance Orbiter, which reached the moon in the summer of 2009.

It took about one year for LRO’s Lunar Orbiter Laser Altimeter (LOLA) to build an elevation map of the entire moon. The altimeter can pinpoint the height of lunar landforms to within four inches! The instrument sends laser pulses to the lunar surface and measures the time that it takes for them to reflect back to the LRO.

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Category: Science