The retroreflectors left on the Moon by Apollo 11, 14, and 15 still return laser pulses fired from Earth, and 57 years of data have measured the Moon's recession at 3.8 centimeters per year while confirming Einstein's general relativity to extraordinary preciā¦
On a quiet night at the Apache Point Observatory in New Mexico, a pulse of green laser light leaves a 3.5-meter telescope, climbs through the atmosphere, and races toward the Moon. About 1.25 seconds⦠[+10957 chars]