Anyone? :confused:

Anyone? :confused:
i really dont know, but my guess is they would use the light from a distant object, or maybe it doesnt have to be that far away. in a dark enviroment, put a sensor of some sort a certain distance from the light source, then when the light is turned on, they would be able to measure distance by the time it took to reach the sensor.
just a guess though.

Hi Muslim,
Here's a short essay on early methods of measuring the speed of light:
Interesting Thing of the Day (http://itotd.com/articles/284/)

...and here's an easy fun way (I haven't tested it, so I don't know if it works for sure):
Measure The Speed of Light With Chocolate and A Microwave (http://physics.about.com/cs/opticsexperiments/a/290903.htm)

They get a stopwatch and flick the light switch then wait for the light to come on. When the light comes on he stops the stopwatch and so they now know the speed of light.

Pete: At first glance I thought you were pulling my leg but it turned out you were conveying very good information.

Muslim: If you will make a Google or Yahoo internet search of " velocity of light" you should get a wealth of references explaining various methods which scientists have used throughout centuries. Pete's method is often obscurely explained in Physics 101 textbooks and certainly is convenient though not so widely recognized. And it can be tasty and nutricious. :cool:

Thanks for the info guys.

The first successful measurement of the speed of light was made by Olaus Roemer in 1676. He noticed that the time between the eclipses of the moons of Jupiter was less as the distance away from Earth is decreasing than when it is increasing. He correctly surmised that this is due to the varying length of time it takes for light to travel from Jupiter to Earth as the distance changes. He obtained a value equivalent to 214,000 km/s.

The first successful measurement of the speed of light using an earthbound apparatus was carried out by Hippolyte Fizeau in 1849. Fizeau's experiment was conceptually similar to those proposed by Beeckman and Galileo. A beam of light was directed at a mirror several thousand metres away. On the way from the source to the mirror, the beam passed through a rotating cog wheel. At a certain rate of rotation, the beam could pass through one gap on the way out and another on the way back. But at slightly higher or lower rates, the beam would strike a tooth and not pass through the wheel. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, the speed of light could be calculated. Fizeau reported the speed of light as 313,000 kilometres per second. Fizeau's method was later refined by Marie Alfred Cornu (1872) and Joseph Perrotin (1900).

Leon Foucault improved on Fizeau's method by replacing the cogwheel with a rotating mirror. Foucault's estimate, published in 1862, was 298,000 kilometres per second. Foucault's method was also used by Simon Newcomb and Albert A. Michelson. Michelson began his lengthy career by replicating and improving on Foucault's method.

In 1926, Michelson used rotating mirrors to measure the time it took light to make a round trip from Mount Wilson to Mount San Antonio in California. The precise measurements yielded a speed of 186,285 miles per second (299,796 kilometres per second).

The first successful measurement of the speed of light was made by Olaus Roemer in 1676. He noticed that the time between the eclipses of the moons of Jupiter was less as the distance away from Earth is decreasing than when it is increasing. He correctly surmised that this is due to the varying length of time it takes for light to travel from Jupiter to Earth as the distance changes. He obtained a value equivalent to 214,000 km/s.

The first successful measurement of the speed of light using an earthbound apparatus was carried out by Hippolyte Fizeau in 1849. Fizeau's experiment was conceptually similar to those proposed by Beeckman and Galileo. A beam of light was directed at a mirror several thousand metres away. On the way from the source to the mirror, the beam passed through a rotating cog wheel. At a certain rate of rotation, the beam could pass through one gap on the way out and another on the way back. But at slightly higher or lower rates, the beam would strike a tooth and not pass through the wheel. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, the speed of light could be calculated. Fizeau reported the speed of light as 313,000 kilometres per second. Fizeau's method was later refined by Marie Alfred Cornu (1872) and Joseph Perrotin (1900).

Leon Foucault improved on Fizeau's method by replacing the cogwheel with a rotating mirror. Foucault's estimate, published in 1862, was 298,000 kilometres per second. Foucault's method was also used by Simon Newcomb and Albert A. Michelson. Michelson began his lengthy career by replicating and improving on Foucault's method.

In 1926, Michelson used rotating mirrors to measure the time it took light to make a round trip from Mount Wilson to Mount San Antonio in California. The precise measurements yielded a speed of 186,285 miles per second (299,796 kilometres per second).

So basically the speed of light is not traveling at a constant speed? or is it that these guy are probably using crap methods?

I mean can't we use lasers or thing to nail it right down to 1 KM?

Hi Muslim,
So basically the speed of light is not traveling at a constant speed?
The speed of light varies according to the medium that it travels through, but that's not the problem here.
The measurements listed were all measuring the speed of light in air or vaccuum (which are very close).

or is it that these guy are probably using crap methods?
The best earlier methods weren't as accurate as the best later methods.

I mean can't we use lasers or thing to nail it right down to 1 KM?
Apparently it can be stopped altogether!