Alright you smart scientist, answer this question...?

Question

I know that speed of light is 300,000,000 meters per second. Now, how did they measure this speed? What equipment did they use to measure the speed of light?

Answer 1

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 a rotating prism 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).

Answer 2

I heard two things. First I remember hearing something about them bouncing light off of the moon and back to earth and measuring how long it took and they came to that conclusion.

I also heard they used a device that could tell when light hit it and they fired up a light pointed at it from a large distance. Then they used a formula and come to 300,000,000 meters per seconds.

just to let you know they rounded it to 300,000,000. It could of been 301,320,210 or something like that.

Answer 3

A clock of some sort, usually.

In the 1670's, the Danish astronomer Ole Roemer was observing Jupiter's moon Io and noticed that it was not always where he expected it to be. He had calcualted how long each orbit would take, but found that sometime Io was "ahead" of where it shoudl be, and sometimes it was "behind". Then he realized that when it was ahead was when the earth was closer to Jupiter, and when the earth was further away, Io would appear to be behind. He used his mearsurements to come up with the rough estimate we use today for c 186k miles/sec (which is 300000000 m/sec.

Amazing, huh?

And yeah the Gallileo thing is wrong. He did try that experiment, but realized it was useless.

Answer 4

first of all thats not the speed of light its like 176,282 miles per sec and they found that out by rigging a pulsating light 2 a rotating mjirror, not quite sure how< then timed when the light how fast the mirror wouls have 2 spin to reflect the light at a constant stream

the guy above mes full of **** reaction times couldnt be trusted 2 something that was that time sensitive

Answer 5

That's a very good question. In the early 17th century, many scientists believed that there was no such thing as the "speed of light"; they thought light could travel any distance in no time at all. Galileo disagreed, and he came up with an experiment to measure light's velocity: he and his assistant each took a shuttered lantern, and they stood on hilltops one mile apart. Galileo flashed his lantern, and the assistant was supposed to open the shutter to his own lantern as soon as he saw Galileo's light. Galileo would then time how long it took before he saw the light from the other hilltop.

Nope. The problem was that the speed of light is simply too fast to be measured this way; light takes such a short time (about 0.000005 seconds, in fact) to travel one mile that there's no way the interval could have been measured using the tools Galileo had.
So what you'd need is a really long distance for the light to travel, like millions of miles. How could someone set up an experiment like that?
Well...during the 1670's, the Danish astronomer Ole Roemer was making extremely careful observations of Jupiter's moon Io. The black dot is Io's shadow. Io makes one complete orbit around Jupiter every 1.76 days; the time it takes to make each orbit is always the same, so Roemer expected that he could predict its motion quite precisely. To his astonishment, he discovered that the moon didn't always appear where it was supposed to be. At certain times of the year, it seemed to be slightly behind schedule; at other times, it was slightly ahead.
That's weird. Why would it orbit more quickly at some times and more slowly at others?


That's exactly what Roemer wondered, and no one could think of any plausible answer. Roemer did notice, however, that Io seemed to be ahead of its predicted orbit when the earth was closer to Jupiter, and behind when it was farther away...


This has got to have something to do with the speed of light, but I don't quite see how it all fits together.


Well, think about this: if light doesn't travel infinitely fast, then it must take some amount of time to get from Jupiter to earth. Let's say it takes an hour. Then when you look at Jupiter through a telescope, what you're actually seeing is light that left an hour ago--so you're seeing what Jupiter and its moons looked like one hour in the past.

Wait a second--I think I see where this is going. When Jupiter was farther away, light would take even longer to get from there to here, so that Roemer was seeing Io as it had been at an even earlier time than usual--maybe an hour and fifteen minutes ago, instead of an hour. And the opposite would happen when Jupiter and the earth were especially close together. So Io wasn't changing its orbit at all; it would just appear to be in different places depending on how long its light had taken to get here.



Very good! Now, knowing how much Io's timing seemed to change and how much the distance from earth to Jupiter varied, Roemer was able to calculate a value for the speed of light. The number he came up with was about 186,000 miles per second, or 300,000 kilometers per second.

In the years that followed, as better equipment and techniques were developed, many other people were able to measure the speed of light more accurately. With the resources of today's technology, we can measure it to an incredibly high precision. For instance, astronauts have attached a mirror to a rock on the moon; scientists on earth can aim a laser at this mirror and measure the travel time of the laser pulse--about two and a half seconds for the round trip. (The idea behind this experiment is not so different from Galileo's, if you think about it...) And anyone who measures the speed of light, at any time, using any method, always gets the same result: just slightly less than 300,000 kilometers per second.


Other kinds of electromagnetic radiation, like radio waves and microwaves, are supposed to travel at the same speed as light. Has their speed been measured also?


Yes; in 1888, more than 200 years after Roemer's observations, Heinrich Hertz generated some electromagnetic waves in his laboratory. He measured their speed and came up with that familiar number, 300,000 kilometers per second--a very strong piece of evidence that light and electromagnetic radiation are the same thing.

Answer 6

That's a very good question. In the early 17th century, many scientists believed that there was no such thing as the "speed of light"; they thought light could travel any distance in no time at all. Galileo disagreed, and he came up with an experiment to measure light's velocity: he and his assistant each took a shuttered lantern, and they stood on hilltops one mile apart. Galileo flashed his lantern, and the assistant was supposed to open the shutter to his own lantern as soon as he saw Galileo's light. Galileo would then time how long it took before he saw the light from the other hilltop.






And then he could just divide the distance by the time to get the speed. Did it work? Nope. The problem was that the speed of light is simply too fast to be measured this way; light takes such a short time (about 0.000005 seconds, in fact) to travel one mile that there's no way the interval could have been measured using the tools Galileo had.



So what you'd need is a really long distance for the light to travel, like millions of miles. How could someone set up an experiment like that?


Well...during the 1670's, the Danish astronomer Ole Roemer was making extremely careful observations of Jupiter's moon Io. The black dot is Io's shadow. Io makes one complete orbit around Jupiter every 1.76 days; the time it takes to make each orbit is always the same, so Roemer expected that he could predict its motion quite precisely. To his astonishment, he discovered that the moon didn't always appear where it was supposed to be. At certain times of the year, it seemed to be slightly behind schedule; at other times, it was slightly ahead.

Hubble Space Telescope image of Jupiter, its satellite Io and Io's shadow







That's weird. Why would it orbit more quickly at some times and more slowly at others?


That's exactly what Roemer wondered, and no one could think of any plausible answer. Roemer did notice, however, that Io seemed to be ahead of its predicted orbit when the earth was closer to Jupiter, and behind when it was farther away...


This has got to have something to do with the speed of light, but I don't quite see how it all fits together.


Well, think about this: if light doesn't travel infinitely fast, then it must take some amount of time to get from Jupiter to earth. Let's say it takes an hour. Then when you look at Jupiter through a telescope, what you're actually seeing is light that left an hour ago--so you're seeing what Jupiter and its moons looked like one hour in the past.


Wait a second--I think I see where this is going. When Jupiter was farther away, light would take even longer to get from there to here, so that Roemer was seeing Io as it had been at an even earlier time than usual--maybe an hour and fifteen minutes ago, instead of an hour. And the opposite would happen when Jupiter and the earth were especially close together. So Io wasn't changing its orbit at all; it would just appear to be in different places depending on how long its light had taken to get here.



Very good! Now, knowing how much Io's timing seemed to change and how much the distance from earth to Jupiter varied, Roemer was able to calculate a value for the speed of light. The number he came up with was about 186,000 miles per second, or 300,000 kilometers per second.

In the years that followed, as better equipment and techniques were developed, many other people were able to measure the speed of light more accurately. With the resources of today's technology, we can measure it to an incredibly high precision. For instance, astronauts have attached a mirror to a rock on the moon; scientists on earth can aim a laser at this mirror and measure the travel time of the laser pulse--about two and a half seconds for the round trip. (The idea behind this experiment is not so different from Galileo's, if you think about it...) And anyone who measures the speed of light, at any time, using any method, always gets the same result: just slightly less than 300,000 kilometers per second.


Other kinds of electromagnetic radiation, like radio waves and microwaves, are supposed to travel at the same speed as light. Has their speed been measured also?


Yes; in 1888, more than 200 years after Roemer's observations, Heinrich Hertz generated some electromagnetic waves in his laboratory. He measured their speed and came up with that familiar number, 300,000 kilometers per second--a very strong piece of evidence that light and electromagnetic radiation are the same thing

Answer 7

Hehe. That actual speed of light is 299792458m/s (read it from a physics book once)

As for your question, it was discovered by Galileo and his assistant. Galileo thought that there was no such thing as the speed of light until him and his assistant flashed his light on the hill tops one mile apart. Galileo flashed his lantern and as soon as his assistant saw the light he would have flashed his too. Galileo times how long it took the light from him to his assistant to get there.

Answer 8

They bounced a laser off a mirror, I believe on the moon, and calculated the distance divided by the time it took to go and come back

Answer 9

try looking for the michaelson/morley experiment using a series of mirrors...
i recall from high school physics about 40 yrs ago...
i think they got a close approximation and a nobel prize.
of course nowadays they bounce lasers off the moon, etc, right?

Answer 10

a very light ruler? one guy stood at one end of a large field that was exactly 3,000 meters with a lighter and another guy stood at the other end with a stop watch...and multiplied by 1,000,000? Um... they are smart?