We all know about earthquakes, but did you know that moonquakes also exist? That’s right, they were first discovered by the Apollo astronauts. Moonquakes are much weaker than the largest earthquakes, though they can last for up to an hour, due to the lack of water to dampen seismic vibrations. Information about moonquakes comes from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972. The instruments placed by the Apollo 12, 14, 15 and 16 functioned perfectly until they were switched off in 1977. The first three kinds of moonquakes mentioned above tend to be mild; however, shallow moonquakes can register up to 5.5 on the Richter scale. Between 1972 and 1977, twenty-eight shallow moonquakes were observed. On Earth, quakes of magnitude 4.5 and above can cause damage to buildings and other rigid structures. Continue reading for more.