How did scientists measure the speed of light ??

Question

this question has been wondering around in my head 4 a while .. thanx :)

Answer 1

The basic concept on how the speed of light was first accurately measured is realy quite simple.

What was done was to set up a reflective octagon. This octagon was then turned at a constant rate. From above the octagon there would be a light source that shines light down onto it. This light is then reflected at an angle of 90 degrees and travels away from the octagon. This light is allowed to travel a long distance, initially the distance between two mountains. It is then reflected back at the octagon with a mirror. When it returns to the octagon it gets reflected downwards. If the octagon is in the right orientation it will reflect the light into a photodetector. If it is not oriented properly it will not hit the photo detector.

So if you know the rotational speed of the octagon in rotations per second, call this N (rot/s). And you know the distance between the two mountains say D. You know that when the octagon makes one eigth of a turn it will line up properly. Now you increase the rotational speed of the octagon until you start to receive pulses of light at the photodetector. Once you do you record the rotational speed. You know that the speed of light can be determined by:

V = 2D / T  (velocity equals distance travelled divided by time taken)

Note that I use twice the distance between the mountains, this is because the light has to travel there as well as back.

Now you also know that while the light was travelling your octagon made one eigth of a revolution and you know the speed in rotations per second. So the time is simply:

T = 0.125 / N      1/8 of a rotation / rot/s

So you can sub this in above to get:

V = 2DN / (0.125)

This will give you the speed of light it you know how far the octagon is from the mirror and how fast the octagon is spinning when you start to pick up your sent pulses back on the photodetector.

Answer 2

http://itotd.com/articles/284/measuring-...

Answer 3

Scientists through telescopes look at the birth of a star, and time how long it takes it's light to reach earth.

Answer 4

It's been done many ways throughout history.  Go wiki "speed of light"

http://en.wikipedia.org/wiki/Speed_of_li...

Today, it's a defined quantity.  If you tried to measure the speed of light any better, all you'd be doing is refining the definition of the meter.

Answer 5

scientific ruler

Answer 6

With a light meter.