A geodetic technique in which a laser signal is transmitted from a ground-based station, reflects off specially designed mirrors (retro-reflectors) placed on the Moon, and is received back at the station.

• A. Moon Laser Ranging
• B. Lunar Reflector Timing
• C. Lunar Orbital Laser Tracking
• D. Lunar Laser Ranging (LLR)

Answer: (D)

The key idea is measuring the distance to the Moon with extreme precision by sending a laser pulse from Earth, letting it bounce off retro-reflectors left on the Moon, and timing how long the round trip takes. This technique is known as Lunar Laser Ranging (LLR). The retro-reflectors rotate with the Moon, but they reflect the light back toward Earth regardless of the Moon’s orientation, allowing accurate distance measurements. Since light travels about 30 cm per billionth of a second, precise timing yields centimeter-level distances and improves models of the Earth–Moon system, lunar rotation, and tests of gravity. Other name options aren’t the standard term used for this method.