Skip to Navigation ↓ Galileo was the first person to attempt to
measure the speed of light. In the early 1600s, he and an
assistant each stood on a different hilltop with a known
distance between them. The plan was for Galileo to open the
shutter of a lamp, and then for his assistant to open the
shutter of a lamp as soon as he saw the light from Galileo's.
Using the distance between the hilltops and his pulse as a
timer, Galileo planned to measure the speed of light. He and his
assistant tried this with different distances between them, but
no matter how far apart they were, Galileo could measure no
difference in the amount of time it took the light to travel and
concluded that the speed of light was too fast to be measured by
this method. He was correct. We now know the speed of light very
precisely, and if Galileo and his assistant were on hilltops one
mile apart, light would take 0.0000054 seconds to travel from
one person to the other. It is understandable that Galileo was
unable to measure this with his