2007-03-23 06:22:46 · 6 answers · asked by silverback7m 2 in Science & Mathematics ➔ Physics
now it is measured with mirrors and physical time domain reflectometry.
2007-03-23 07:14:16 · answer #1 · answered by Anonymous · 1⤊ 0⤋
Light is shined onto a rotating mirror. When the angle is right, the light reflects to a distant (fixed) mirror and is reflected straight back. But... by the time the light reaches back to the rotating mirror the mirror is no longer at the same angle, so the light is reflected back at a slightly different angle. If the reflected light is mixed with the incident light, they interfere with each other (as waves out-of-phase) and a diffraction pattern is developed. The diffraction lines can be measured, and if the speed of rotation is known, and the distance to the far mirror is known, the speed of light can be measured.
That's pretty much how Michelson and Morley did it the first time, too.
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2007-03-23 13:30:24 · answer #2 · answered by tlbs101 7 · 2⤊ 0⤋
1. In the 1670's, the Danish astronomer Ole Roemer has found of way to measure the speed of light. Please see [1] for long but a good explanation.
2 For a little entertainment see reference [2 and 3]
3. A little history[ see 4]
4. How you can do it today [see 5]
2007-03-23 13:34:12 · answer #3 · answered by Edward 7 · 0⤊ 0⤋
There have been various measurement of the speed since 1676. Olaus Roemer used observations of Jupiter's satellites.
See the links for more information.
2007-03-23 13:35:30 · answer #4 · answered by morningfoxnorth 6 · 1⤊ 0⤋
they shined a bright light at a mirror and measured how long it took to go to the mirror and reflact back and calculated the speed from that
2007-03-23 14:25:46 · answer #5 · answered by 22 4 · 1⤊ 0⤋
using Michelson's interferometer
2007-03-31 02:25:08 · answer #6 · answered by neo 1 · 0⤊ 0⤋