The Apollo 11 astronauts did not leave the moon unchanged. Besides some footprints and a flag, there was some equipment left on the moon, including a mirror pointed towards the earth. Earth based scientists measure the distance to the moon by firing a laser pulse at the mirror and measuring the time it takes for the laser pulse to return to earth.
How long does it take in seconds for an short laser pulse to bounce off the moon and come back?
How long does it take in seconds for an short laser pulse to bounce off the moon and come back?
Details and assumptions
- The moon is, on average, 385,000 km away from the earth
- The speed of light is approximately
3×10 8 m/s, - Note: This experiment, the Lunar Laser Ranging Experiment, is one of the most accurate distance measurements ever made. For example, one can determine that the moon is moving away from the earth at a rate of 3.8 centimeters per year.
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