who determined the speed of light? how ?

Question

Also, how and who determined light-years?

Answer 1

http://galileo.phys.virginia.edu/classes/109N/lectures/spedlite.html
and
http://itotd.com/articles/284/measuring-the-speed-of-light/

outline some ways it was done in history

maxwell's work would not have come up with a number without experiments, since the permeability and permittivity of free space need measurement and are not derivable. it was more that the permeability and permittivity of free space were determined by measuring the speed of light


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http://en.allexperts.com/q/Astronomy-1360/light-year-info-1.htm

Answer 2

In 1667, Galileo is often credited with being the first scientist to try to determine the speed of light. His method was quite simple. He and an assistant each had lamps which could be covered and uncovered at will. Galileo would uncover his lamp, and as soon as his assistant saw the light he would uncover his. By measuring the elapsed time until Galileo saw his assistant's light and knowing how far apart the lamps were, Galileo reasoned he should be able to determine the speed of the light. His conclusion: "If not instantaneous, it is extraordinarily rapid". Most likely he used a water clock, where the amount of water that empties from a container represents the amount of time that has passed. Galileo just deduced that light travels at least ten times faster than sound.


[SPEED OF LIGHT] 1675 Ole Roemer: 200,000 Km/sec

In 1675, the Danish astronomer Ole Roemer noticed, while observing Jupiter's moons, that the times of the eclipses of the moons of Jupiter seemed to depend on the relative positions of Jupiter and Earth. If Earth was close to Jupiter, the orbits of her moons appeared to speed up. If Earth was far from Jupiter, they seemed to slow down. Reasoning that the moons orbital velocities should not be affected by their separation, he deduced that the apparent change must be due to the extra time for light to travel when Earth was more distant from Jupiter. Using the commonly accepted value for the diameter of the Earth's orbit, he came to the conclusion that light must have traveled at 200,000 Km/s.

Answer 3

From Wikipedia:
"The fourteenth century Indian scholar Sayana wrote in a comment on verse Rigveda 1.50.4 (1700–1100 BCE—the early Vedic period): "Thus it is remembered: [O Sun] you who traverse 2202 yojanas{I yojana is about 9 miles} [ca. 14,000 to 30,000 km] in half a nimesa [ca. 0.1 to 0.2 s]", corresponding to between 65,000 and 300,000 km/s, for high values of yojana and low values of nimesa consistent with the actual speed of light"

That's a very large range of values, but indicates a finite speed, and the high value is what we use for an approximation today.

"However, by 1950 repeated measurements by Essen established a result of 299,792.5±1 km/s; this became the value adopted by the 12th General Assembly of the Radio-Scientific Union in 1957."

The light year is arrived at by simply multiplying the speed of light by the number of seconds in a day, and the number of days in a year. A light year is an enormous distance, approximately 9,460,963,590,000,000 km ± 5,000,000 km The first person to calculate and apply the light year is not mentioned.

Answer 4

light is approximately 300,000 km/sec, in one hour 1,079,252,848.8 km, in one light year roughly 9.46×10^12km,.