what is the speed of light?
339050
The speed of light in a vacuum is exactly 299,792,458 metres per second (or 1,079,252,848.8  km·h-1, which is approximately 186,282.397 miles per second, or 670,616,629.4 miles per hour). This value is denoted by the letter c, reputedly from the Latin celeritas, "speed". Note that this speed is a definition, not a measurement, since the fundamental SI unit of distance, the metre, has been defined since 1983 in terms of the speed of light—one metre is the distance light travels in a vacuum in 1/299,792,458 of a second. The speed of light through a transparent medium (that is, not in vacuum) is less than c; the ratio of c to this speed is called the refractive index of the medium.
63805
Actually there is no speed of dark.\nBut according to me it should be the same as the speed of light because as soon as the light goes the dark appears.So it must be as the speed of light i.e. 3* 10^8 meters/seconds
859647
The speed of light is an illusion imposed upon us by the Almighty. He lets you see the light whenever He wants you to.
932886
the speed of light = 299 792 458 m / s or 1079252848800 M/H\ncircumference = 2*Pi*R \nso 2* 3.14159*R= 107925848800M/H\n1079252848800/(2*3.14159)=R\nRadius= 1.71768571 × 1011(<--- times 10 to the 11th power) meters
263654
The speed of light is exactly 299,792,458 m/s.\nThe meter is defined in terms of the distance which light travels in a certain amount of time, that is how we know the EXACT speed of light....we defined it as so.
283556
The speed of light is a CONSTANT and has the symbol c in Science and is measured in meters per second.\n\nc (the speed of light) is equal to 3 times 10 to the power 9.\n\nNow 3x10*9 meters per second equals 3000000000 meters per second. (3 then nine zeroes!).\n\nc is important in physics because nothing can go faster than  c. \n\nNothing can go faster than the speed of light and as Einstein showed with the Theory of Relativity (a very important theory in physics) when an object (mass if you will) approaches c it gets bigger and bigger!! \n\nIf it gets to c then its mass will become infinite - this is impossible! An object with infinite mass! Hence it is impossible to reach the speed of light. \n\nHope this helps.
219832
The speed of light is indeed a constant.  What's important is that it is a constant to every observer.  If you are traveling toward a light source at 1000 m/s, you will measure the light's velocity at 300,000 m/s.  If you are traveling AWAY from the light source, it will still measure 300,000 m/s.\n\nLight IS the absolute speed limit. (Of this universe anyway)
753670
The speed of light varies depending on the medium the light is traveling through.  In a vacuum however, which is the fastest medium in which light can travel, the speed of light is 299,792,458 m/s.
44523
the speed of light(radiation) is a constant and equals the wavelength times the frequency. As wavelength gets longer the freq goes down and vice versa.
1186727
It is a failing of the current theories of physics that the values of the key fundamental constants - of which c is one - cannot be derived but have to be measured and inserted into the equations. In other words, no-one knows what determines the speed of light.\n\nIt is true that the permittivity and permeability of free space are related to the speed of light, but the relationship is the other way around - they are what they are because the speed of light is what it is.\n\nThere have been two sources of thoughts that the speed of light may vary over time. One is theoretical, because it may help the sums work better when describing the early universe (i.e. moment after the big bang).\n\nThe other is experimental, and is controversial as it has not been independently confirmed (see link). This involves looking at light from galaxies so far away the light took billions of years to reach us - ie we are looking back to the early universe. But the measurements show a change in the fine structure constant, and not c directly, so there could be other sources of the discrepancies if the measurements are correct.
492088
The speed of sound isn't even close to the speed of light. The speed of sound in air is usually given as 343 meters per second at sea level in air and the speed of light is approximately 3 X 10^8 meters per second (300,000,000 m/s)in a vaccuum.
532772
nothing but light can travel at light speed.  the faster you go, the more energy it requires to accelerate.  at speeds that are close to the speed of light, you would need what is basically an infinite amount of power to accelate.  with current technology, it is impossible.  the only reason light can travel that fast, is because when it is created it is already traveling that fast.  it doesnt have to accelerate.
1103100
Here's the equation T = T' / sqrt[1- (v^2/c^2)]\n\nT is time measured by an observer at rest.  T' (read: T prime) is time measured by a moving observer.  v is the moving observer's velocity and c is the speed of light.\n\nThe speed of light is very fast.  So if v is 100 mph or 10 000 mph when you divide it by a number like c (186000 mps that's miles per second so a huge amount of miles per hour)  the v^2/c^2 value is zero and T = T'/sqrt (1) which is T = T'/1 so there is no measurable difference.  \n\nBut plug in 9/10 c for v.  That means an object going 9/10 the speed of light.  You get T = T' / sqrt[1-(9/10c)^2/c^2]\n\nc^2 cancels out and you get T = T'/[sqrt 1-(81/100)] T would be 2.2 times T'.  More time transpired for the non moving observer.\n\nHow did we get the equation?  Einstein was really smart.
418308
The speed of light in a vacuum is exactly 299,792,458 metres per second (or 1,079,252,848.8  km·h-1, which is approximately 186,282.397 miles per second, or 670,616,629.4 miles per hour).
183503
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, which gives about 3.00E8 m/s for the speed of light.\n\nIts speed can also be derived from Maxwell's equations for the speed of propagation of electromagnetic fields in vacuum.
886711
The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning "swiftness". It is the speed of all electromagnetic radiation in a vacuum, not just visible light.\n\nIn metric units, c is exactly 299,792,458 metres per second (1,079,252,848.8 km/h). Note that this speed is a definition, not a measurement, since the fundamental SI unit of length, the metre, has been defined since October 21, 1983 in terms of the speed of light: one metre is the distance light travels in a vacuum in 1/299,792,458 of a second. Converted to imperial units, the speed of light is approximately 186,282.397 miles per second, or 670,616,629.384 miles per hour, or almost one foot per nanosecond.\n\nThrough any transparent or translucent material medium, like glass or air, it has a lower speed than in a vacuum; the ratio of c to this slower speed is called the refractive index of the medium (the actual speed is not affected, the speed of light is constant, the fact that the light is reflected around inside the glass will make a greater amount of time necessary for it to reach the next point). Changes of gravity, however, warp the space the light has to travel through, making it appear to curve around massive objects. This gives rise to the phenomenon of gravitational lensing, in which large assemblies of matter can refract light from far away sources, so as to produce multiple images and similar optical distortions.\nclick here:http://en.wikipedia.org/wiki/Speed_of_light#Overview
327223
1 lightyear is the distance a beam of light can travel in a vacuum in one year.  Given that the speed of light is roughly 3*(10^8) meters per second, or about 670.6 million miles per hour, then 93 million miles is about 1.58*(10^-5) lightyears.  Another way to look at it, is that it takes about 7.21 minutes for light from the sun to reach earth, and they are roughly 93 million miles apart.