Lunar Laser Ranging Experiment - Results

Results

Some of the findings of this long-term experiment are:

  • The Moon is spiraling away from Earth at a rate of 3.8 cm per year. This rate has been described as anomalously high.
  • The Moon probably has a liquid core of about 20% of the Moon's radius.
  • The universal force of gravity is very stable. The experiments have put an upper limit on the change in Newton's gravitational constant G of less than 1 part in 1011 since 1969.
  • The likelihood of any "Nordtvedt effect" (a composition-dependent differential acceleration of the Moon and Earth towards the Sun) has been ruled out to high precision, strongly supporting the validity of the Strong Equivalence Principle.
  • Einstein's theory of gravity (the general theory of relativity) predicts the Moon's orbit to within the accuracy of the laser ranging measurements.

The presence of reflectors on the Moon has been used to rebut claims that the Apollo landings were faked. For example, the APOLLO Collaboration photon pulse return graph, shown here, has a pattern consistent with a retroreflector array near a known landing site.

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