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Tuesday, February 10, 2015

How long does it take for moonlight to reach the earth?

Light travels through space at just over 186,000 miles per second. The moon is just under 250,000 miles from Earth, so light from the Moon's surface has to travel more than one second (about 1.3 seconds) to reach us.

The astronauts left reflecting mirrors on the moon. By shining a laser beam on those mirrors from Earth, and measuring the time (less than 3 seconds) it takes to see its reflection, the length of the round trip can be easily calculated to within a few inches!