The Apollo astronauts placed special reflector arrays on the Moon (Fig. P23.61A). The array was comprised of “corner reflector” prisms that have the property of reflecting a beam of light exactly back along its incoming path. Using the Apache Point Observatory Lunar Laser-Ranging Operation (Fig. P23.61B), powerful laser pulses are directed at the Moon, and the time it takes them to reflect back is measured.
(a) If the time of reflection can be measured to an accuracy of one-hundredth of a nanosecond, what is the uncertainty in the measured Earth-Moon distance?
(b) A 2.3-W laser is used to get a very faint reflected pulse. When the laser’s beam reaches the lunar surface, it is approximately 2.0 km in diameter. What is the intensity of the laser light at the Moon’s surface, and how does it compare to sunlight there? Is shooting the Moon with this laser destructive to the lunar surface?