How much time would it take for a ray of light to travel between the two hills?

Question

Galileo tried to measure the speed of light by having two people stand on hills about 5km apart. Each

would hold a shuttered lantern. The first would open his lantern and when the second saw the light,

he would open his lantern. The first person would then measure how much time it took between the

time he first opened his lantern and when he saw the light returning.

How much time would it take for a ray of light to travel between the two hills?

Would this be a plausible method of measuring the speed of light?

How far apart, at a minimum, would recommend two hills be, for such a method to work?

Answer 1

Hi,

The answer is actually quite simple. If the distance between the hills is X and the speed of light is C, it would take time X/C which is just an application of the speed formula.

Now, how far apart should they be is more a biological question. Humans can only perceive two things as different if they are at least (1/20) seconds (the literature differs a little on the exact number). So the time difference between the two shutters must be at least (1/20) seconds. Plug this in for the time. (1/20) = X/C is then solved for X to give you the minimum distance.