Which lunar ranging technique is used to measure distance to the Moon?

Which lunar ranging technique is used to measure distance to the Moon?

• A. Lunar Laser Ranging (LLR)
• B. Satellite Laser Ranging (SLR)
• C. Very Long Baseline Interferometry (VLBI)
• D. DORIS

Answer: (A)

Measuring distance to the Moon uses timing a light signal to determine how far away it is. Lunar Laser Ranging does this by sending powerful laser pulses from Earth to retroreflector arrays placed on the Moon. The light bounces back, and measuring the round-trip time with knowledge of the speed of light gives the Earth–Moon distance with very high precision, at the centimeter level over time. This technique is built specifically for the Moon, using those lunar reflectors to produce direct time-of-flight measurements. Other methods don’t target the Moon in the same way. Satellite Laser Ranging measures distances to artificial satellites in orbit around Earth, not to the Moon. Very Long Baseline Interferometry uses radio signals to determine angular positions and baselines between observatories, not the direct light travel time to the Moon. DORIS is a Doppler-based system for tracking satellites and precise positioning, also not used for lunar distance via laser timing.

Measuring distance to the Moon uses timing a light signal to determine how far away it is. Lunar Laser Ranging does this by sending powerful laser pulses from Earth to retroreflector arrays placed on the Moon. The light bounces back, and measuring the round-trip time with knowledge of the speed of light gives the Earth–Moon distance with very high precision, at the centimeter level over time. This technique is built specifically for the Moon, using those lunar reflectors to produce direct time-of-flight measurements.

Other methods don’t target the Moon in the same way. Satellite Laser Ranging measures distances to artificial satellites in orbit around Earth, not to the Moon. Very Long Baseline Interferometry uses radio signals to determine angular positions and baselines between observatories, not the direct light travel time to the Moon. DORIS is a Doppler-based system for tracking satellites and precise positioning, also not used for lunar distance via laser timing.