how to measure the speed of light
The speed of light is- 299 792 458 meter / per second
how to measure the speed of light EASY 101 - follow a beam of light for one year. Now, using a laser rangefinder/radar gun shoot a beam back to the beams source and take a reading off the viewscreen.
It is about 2.99792458 * 10^6 m/s in a vacuum (from google). However, the speed of light depends on the permeability and permittivity of an substance, so this speed decreases in different substances. c = 1/sqrt(epsilon*mu) with mu being the permeability and epsilon being the permittivity. You could measure it by shooting a beam of light from a source and detecting it at an arbitrary distance x away. The speed would be equal to x divided by the time it took for it to reach the destination. This would be most accurate if the source and destination were at rest relative to each other to assure that they would share the same time (according to the theory of relativity).
There are many techniques to measure the speed of light. The first measurement of light-speed on Earth was by Armand Fizeau in 1849. He used a beam of light reflected from a mirror 8 km away. The beam passed through the gaps between teeth of a rapidly rotating wheel. The speed of the wheel was increased until the returning light passed through the next gap and could be seen. Then c was calculated to be 315,000 km/s. Leon Foucault improved on this a year later by using rotating mirrors and got the much more accurate answer of 298,000 km/s. His technique was good enough to confirm that light travels slower in water than in air. The wikipedia link below will help you...
3.00 x 10^8 m/s but that is just in a vacuum. The speed of light changes through different mediums (slightly though), that is why you see rainbows through prisms. measuring the speed of light requires some thinking, I am not really sure how they get that. through experiments, physicists have found that all waves on the electromagnetic spectrum travel at the speed of 3.00 x 10^8 m/s. Those waves are also commonly referred to light waves. Only a tiny bit of the electromagnetic spectrum can actually be seen... so if they are going to measure light, it would not be through the naked eye. They would have to be using gadgets that catches frequencies of different waves, that is for sure. Light is a form of energy, and physicists and other scientist use this fact to measure the amount of light. Astronomers use the properties of light to study far away celestial bodies and find out what are they made out of. Chemists use the fact that light is a source of energy when it comes to quantum mechanics to study the properties of electrons in an atom. Photographers use the properties of light to take the best shot (just like astronomers). They must calculate how much light (measure in lumens or candelas, i forgot) to determine shutter exposure. so light can be calculated in many forms and ways... i just don't know any.
