NASA
Apollo 11 astronaut Buzz Aldrin stands next to a seismometer on the Moon in Jul. 1969./Courtesy of NASA

In July 1969, Apollo 11 astronauts Neil Armstrong and Buzz Aldrin first stepped on the moon and planted the U.S. flag. The photo shows Buzz Aldrin standing next to the lunar seismometer at that time. According to the National Aeronautics and Space Administration (NASA), during the Apollo lunar landing mission, a seismometer was installed on the moon to analyze and revealed for the first time that an astonishing number of 'moonquakes' occurred within 100 kilometers of the moon's surface. Data recorded between 1972 and 1977 detected 62 moonquakes. If there were apartments on the moon, they would shake enough to rattle homes, and they were found to shake much longer than earthquakes on Earth. The exact cause of moonquakes has not yet been determined. However, a leading hypothesis includes tidal gravity due to Earth's gravity and relative heating. NASA noted that regardless of the cause, any future residential facilities built on the moon must be designed to withstand such frequent shaking.