what is the exact speed of light?
344154
Scientists have defined the speed of light in a vacuum to be exactly 299,792,458 meters per second (about 186,000 miles per second).\n\nThis definition is possible because since 1983, scientists have known the distance light travels in one second more accurately than the definition of the standard meter. Therefore, in 1983, scientists defined the meter as 1/299,792,458, the distance light travels through a vacuum in one second. This precise measurement is the latest step in a long history of measurement, beginning in the early 1600s with an unsuccessful attempt by Italian scientist Galileo to measure the speed of lantern light from one hilltop to another.\nMicrosoft ® Encarta ® 2006. © 1993-2005 Microsoft
329962
Here is the correct answer....the speed of light is constant IN A VACUUM.  Light is most certainly slowed down by matter, and can be shifted by gravity.
979220
Albert Einstein answered this question a long time ago.  He theorized (and every experiment since then has borne him out) that the speed of light is constant from ANY inertial (non-accelerating) frame of reference.  This includes the speed of light relative to your headlights.  \n\nLight speed is constant.  What changes is time and length.  Weird but true.
54308
As you travel faster and faster, time for you slows down, and length contracts. From your point of view, when you measure the speed of light, it will always be the same. An observer standing still with respect to you and the beam of light could measure your speed at 185000 mps and the speed of light as 186000 mps, and say the difference in speed is 1000 mps. But that is relative to them. The speed of light will always be the same for whoever measures it, no matter how fast they are moving.\n\nSee the website below for more about relativity.
666698
The speed of light in a vacuum is exactly 299,792,458 metres per second (or 1,079,252,848.8  kilometres per hour, which is approximately 186,282.397 miles per second, or 670,616,629.4 miles per hour). \nThe speed of sound c (from Latin celeritas, "velocity") varies depending on the medium through which the sound waves pass.
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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.
381943
As the others have said, all light travels at exactly the same speed.  This is even true if the observer and/or the  light source are moving very very fast.  Once this was proved by experiment, everyone was very upset until Einstein figured it out and showed that time and space can distort. If you want a real bad headache, you can read all about this.  If it doesn't give you a headache, become a physicist!
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10% of the speed of light is roughly 1,116,000 mph (186,000 mp/sec * .1 and then mult by 60).\nIt is roughly 1,796,000 kph.
990328
The speed of light is always constant in any reference frame.\n\nNo matter the reference frame, an observer will always measure the speed of light in a vacuum to be exactly,\n299,792,458 m/s.
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You can't go at the speed of light. It's a theorical limit, so it's unreacheable. Only the light can reach it.\n\nIf C is the speed of light, the fastest you can get is C*0.999999999... (insert as many '9' as you want). When you turn on the headlights, they will be somewhat faster: they'll reach the speed of light.
410856
Engery\nMass\nc is the speed of light (why c? I don't know does anybody else?)
676715
The speed of light is the upper limit of speed in our space-time universe. Nothing here can be faster. And no car or any other macroscopic object can be equal to the speed of light. But the question is a thought experiment, hence, a good one indeed. Questions like this were raised by Einstein and Relativity became part of modern physical theory.\n\nSince the speed of light is an upper limit, the light from the headlamp of the relativistic car cannot be faster than the car. You won't see them in front.
406703
the speed of light is c=3*10 at the 8-th power  m/s\ndark means 0 light
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The speed of light is Warp 1\n\n2xspeed of ;ight is warp 2\n\nand so on and so forth.
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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).
337266
Um, well it depend on how you consider light. If you consider it as a stream of photons, then you might say that if you measure the positions of each of those photons it doesn't have velocity.\nIf you say it is a wave and always in motion then it is not relative to your velocity, exactly. Even if you were travelling at 30000000mph the light would still appear to be travelling at 3x10to the power of 8 m/s away from you. Light is the fixed speed limit for the universe. But at the far reaches where the material of space itself is expanding into nothing, it is expanding at a speed greater than the speed of light because that speed limit only applies to objects moving within the universe.