, a lunar distance
(LD) is a measurement of the distance from the Earth
to the Moon
. The average distance from Earth to the Moon is 384,403 kilometers (238,857 miles)
High-precision measurements of the lunar distance are made by measuring the time taken for light to travel between LIDAR stations on Earth and retroreflectors placed on the Moon.
The Moon is spiraling away from Earth at an average rate of 3.8 cm per year, as detected by the Lunar Laser Ranging Experiment.
The first person to measure the distance to the Moon was the second-century BCE astronomer and geographer Hipparchus, who used simple trigonometry. He was approximately 26,000 km off the actual distance, an error of about 6.8%.