Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                                2019 July 21

                       Moonquakes Surprisingly Common
                     Image Credit: NASA, Apollo 11 Crew

   Explanation: Why are there so many moonquakes? Analyses of seismometers
   left on the moon by the Apollo moon landings reveals a surprising
   number of moonquakes occurring within 100 kilometers of the surface. In
   fact, 62 moonquakes were detected in data recorded between 1972 and
   1977. Many of these moonquakes are not only strong enough to move
   furniture in a lunar apartment, but the stiff rock of the moon
   continues to vibrate for many minutes, significantly longer than the
   softer rock earthquakes on Earth. The cause of the moonquakes remains
   unknown, but a leading hypothesis is the collapse of underground
   faults. Regardless of the source, future moon dwellings need to be
   built to withstand the frequent shakings. Pictured here 50 years ago
   today, Apollo 11 astronaut Buzz Aldrin stands beside a recently
   deployed lunar seismometer, looking back toward the lunar landing
   module.

                       Tomorrow's picture: moon circle
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                      A service of: ASD at NASA / GSFC
                             & Michigan Tech. U.
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