First, it's just too big. ""Its too big to have been captured by the Earth. The chances of such a capture having been effected and the moon then having taken up nearly circular orbit around our Earth are too small to make such an eventuality credible." -- Issac Asimov Second, it just so happens to be the same apparent size as the Sun causing total eclipses of the Sun and Moon. "There is no astronomical reason why the moon and the sun should fit so well. It is the sheerest of coincidences, and only the Earth among all the planets is blessed in this fashion." -- Issac Asimov Third, like many of the Libs here, the Moon is not very dense. The moons mean density is 3.34 gm/cm3 (3.34 times an equal volume of water) whereas the Earths is 5.5. "If the astronomical data are reduced, it is found that the data require that the interior of the moon is more like a hollow than a homogeneous sphere." -- Dr. Gordon MacDonald, NASA "...the Lunar Orbiter experiments vastly improved our knowledge of the moons gravitational field... indicating the frightening possibility that the moon might be hollow." -- Dr. Sean C. Solomon, MIT The best explanation [for the Moon] was observational errorthe Moon does not exist. -- Irwin Shapiro, Harvard Smithsonian Centre for astrophysics. Fourth, it rings like a bell when you drop things on it. On November 20, 1969, the Apollo 12 crew jettisoned the lunar module ascent stage causing it to crash onto the moon, seismometers left on the Moon reported that the moon reverberated like a bell for more than an hour. Apollo 13 dropped its Third Stage booster onto the lunar surface and the seismometers reported reverberations that lasted for three hours and twenty minutes and traveled to a depth of twenty-five miles, leading to the conclusion that the moon has an unusually lightor even nocore. Ken Johnson, NASA said that the engineers thought the vibrations peculiar, as it the Moon had dampening struts.