How Long Does It Take For A Laser Beam To Reach The Moon?

Key Points:

• The Moon orbits Earth at an average distance of about 238,855 miles, varying between 226,000 and 251,000 miles depending on its position, and is roughly one-third the diameter of Earth.
• Laser beams, made of coherent photons, travel at the speed of light (approximately 670 million miles per hour) and take between 1.21 and 1.35 seconds to reach the Moon, depending on its distance.
• Since 1969, five retroreflector panels with corner cube mirrors have been placed on the Moon by Apollo missions and Soviet rovers to reflect laser beams back to Earth, enabling precise measurements of the Earth-Moon distance.
• These laser ranging experiments have revealed that the Moon is gradually drifting away from Earth at about 1.5 inches per year.
• To improve measurements, NASA's Lunar Reconnaissance Orbiter deployed a new reflector in 2009, which was successfully targeted by laser beams for the first time in 2020 after years of effort.