[OmahaFields]

Actually, you measure the incoming angle from the starlight at two opposite positions of the earths orbit and using the incoming angle and the earth's speed the speed of light was calculated. Done about 200 years ago but they got within about 1%.

[RightWhale]

That is a two-clock method.

[MineralMan]

"Actually, you measure the incoming angle from the starlight at two opposite positions of the earths orbit and using the incoming angle and the earth's speed the speed of light was calculated. Done about 200 years ago but they got within about 1%."

---

Not really close enough I'm afraid, and it ignored the effect of gravity on the distance the light traveled. While it did result in a decent approximation, it was a flawed measurement.

[RadioAstronomer]

From here:

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html

"In 1728 James Bradley made another estimate by observing stellar aberration, being the apparent displacement of stars due to the motion of the Earth around the Sun. He observed a star in Draco and found that its apparent position changed during the year. All stellar positions are affected equally in this way. This distinguishes the effect from parallax which affects nearby stars more noticeably. A useful analogy to help understand aberration is to imagine the effect of motion on the angle at which rain falls. If you stand still in the rain when there is no wind it comes down vertically on your head. If you run through the rain it appears to come at you from an angle and hit you on the front. Bradley measured this angle for starlight. Knowing the speed of the Earth around the Sun he found a value for the speed of light of 301,000 km/s."