: During Apollo 12, NASA deliberately crashed a Lunar Module into the surface. Seismic instruments recorded that the Moon vibrated for over an hour. Wilson argued a natural rocky body would dampen these waves, whereas a hollow metal hull would ring.
Wilson points out that despite varying diameters, lunar craters are surprisingly shallow. He suggests this is due to an "inner hull" made of an ultra-tough metallic substance that prevents deep penetration by meteors. Why the PDF Remains Popular Today
The original 1975 publication is out of print, making digital copies (PDFs) the primary way new readers access this material.
The book discusses the high concentration of refractory metals like titanium in lunar soil, arguing that such a "hull" would be necessary to protect a spaceship from meteors and temperature extremes. The Soviet Connection
books on the subject of alternative lunar theories.
The celestial body orbiting Earth has inspired countless myths, but few theories are as provocative as the one presented in by Don Wilson. Published in the mid-1970s, this work remains a cornerstone of "ancient astronaut" literature and "Hollow Moon" theories. For many seekers of alternative history, finding a PDF version of this book is the first step into a rabbit hole of lunar anomalies and extraterrestrial possibilities. The Core Premise: An Artificial Satellite?
: One of the most famous pieces of evidence cited is the seismic reaction of the Moon. When the Apollo 12 and 13 lunar modules or rockets crashed into the lunar surface, NASA reported that the Moon "rang like a bell" for hours. Wilson argues this indicates a hollow, metallic hull rather than a solid rocky core. Surface Hardness and Composition