The Hollow Moon Theory suggests that the Moon is not a solid natural satellite, but rather has a hollow interior. This idea is considered a fringe conspiracy theory and lacks scientific backing. There are a few key points that proponents of this theory often discuss:

1. Unusual Density: Supporters argue that the Moon’s density is lower than that of Earth, implying it could be hollow. They cite seismic data from lunar missions, which recorded vibrations lasting much longer than expected, leading to the claim that the Moon “rang like a bell.”

2. Alien or Artificial Origins: Some versions of the theory propose that the Moon is an artificial structure, possibly built by extraterrestrial beings. This speculation is based on the belief that the Moon’s perfectly circular orbit and its size relative to Earth are too coincidental.

3. Seismic Evidence: In 1969, NASA’s Apollo missions deployed seismic instruments on the Moon. When a module was deliberately crashed, it caused vibrations that persisted longer than on Earth. Hollow Moon theorists interpret this data as evidence that the Moon is not solid.