Longest laser ranging experiment
The McDonald Laser Ranging Station
United States (Near Fort Davis)
The McDonald Laser Ranging Station, near Fort Davis, Texas, USA, uses a laser to measure the distance between the Earth and the Moon to an accuracy of 1 cm (0.39 inches). It bounces a laser off reflective targets left on the lunar surface by three US Apollo missions and two Soviet Lunokhod missions. The distance between the centres of the Earth and the Moon is 385,000 km (239,000 miles), and the laser ranging has shown that the Moon is receding from the Earth at a rate of 3.8 cm (1.5 inches) per year. This is one of the most accurate distance measurements ever made.