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Old 08-03-2010, 05:36 PM   #45
dreamweaver
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The quote about the moon "ringing like a bell" comes from this guy incidentally:

http://www.physorg.com/news63645811.html

Quote:
As NASA envisions it, astronauts will return to the moon within the next decade or so. Unlike in the earlier, quick, Apollo visits, these astronauts will build a permanent base and prepare for an historic undertaking that will send explorers to Mars. As Clive Neal, associate professor of civil engineering and geological sciences at the University of Notre Dame, envisions it, these same astronauts may be in for a shocking — and rocking — surprise.

Neal and a team of 15 other planetary geologists have reexamined data from seismometers placed by Apollo astronauts at lunar landing sites from 1969 to 1972. They found that instruments from Apollo missions 12, 14, 15 and 16 consistently radioed back seismic data to Earth until they were turned off in 1977 in a NASA cost-cutting measure.

Neal and his colleagues discovered a surprising number of relatively large “moonquakes,” including some that lasted a remarkably long time.

“The moon is seismically active,” Neal said. “When a quake occurs, the moon rings like a bell.”

There are four different types of moonquakes. Deep moonquakes, occurring at roughly 700 kilometers below the surface, were most likely caused by lunar forces triggered by the effect of Earth’s gravity. Other quakes were caused by vibrations from the impact of meteorites, and “thermal quakes” were caused when the frigid crust of the moon expanded when struck by the morning sun after two weeks of deep-freeze lunar night. The first three classes of moonquakes were generally mild.

However, shallow quakes, which occurred only 20 or 30 kilometers below the surface, were another story. They were powerful and long-lasting.

“Between 1972 and 1977, the Apollo seismic data detected 28 shallow quakes,” Neal said. “A few of the shallow quakes registered up to 5.5 on the Richter scale. A magnitude 5 quake on Earth can move heavy furniture and crack plaster.”

Neal points out that vibrations from most earthquakes cease in less than a minute. The biggest earthquakes stop shaking in less than two minutes. The shallow quakes on the moon produced movement that continued for more than 10 minutes.
He's just saying that the moon resonates. There's no sign that he believes this is because the moon is hollow.

I've no opinion either way on whether it is hollow or not, I'm just saying that the guy who used that expression was only commenting on the moon's resonance properties.
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