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Asked by harrysa to Adam, Catherine, Karen, Leila, Nazim on 10 Mar 2012.
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Adam Stevens answered on 10 Mar 2012:
That depends what it’s moving in…!
The speed of light in a vacuum (i.e. going through nothing) is meant to be an absolute universal constant (although the neutrino people at OPERA in Italy may tell you different). If you want the value, google is pretty good for that! https://www.google.co.uk/search?q=speed+of+light
However, as soon as light starts moving /through/ something, it slows down. Materials with different properties change the speed different amounts. For example, light travels slower through glass than through air, which is why it refracts when it hits a window. Some physicists managed to get light to go really really slow by shining it through a particular type of material called a Bose-Einstein condensate. In this case it goes about 40 miles an hour, so technically you’ve probably gone faster than light at some point!
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Catherine Rix answered on 10 Mar 2012:
The speed of light (in a vacuum, where there are no molecules to slow it down) is 299,792,458 meters per second – pretty fast!
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Karen Masters answered on 10 Mar 2012:
In a vacuum light travels about a foot (third of a metre) in one nano second – which is really fast. It takes 8 minutes to get here from the surface of the Sun, about 3 years from the nearest star, and millions of years from our neighbouring galaxies.
For an exact number use Google, or your text book. I always just remember 300,000 km/s which is accurate enough for me, and in the most useful units for an astronomer – because we tend measure the speed galaxies are moving away from us (because of the expansion of the universe) in kilometres per second too.
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Leila Battison answered on 10 Mar 2012:
The *exact* speed of light, according to Google 😉 is 299,792,458 m/s, and its the fastest anything can travel in the universe as far as we know. That’s ten million times faster than a cheetah can run, and one hundred thousand times faster than the speed of sound. So pretty fast!
The boffins at CERN (the big donut in Switzerland that is recreating the conditions of the big bang) thought they had found neutrinos, which are a kind of particle that makes up atoms, that were arriving quite a bit faster than they should have, and going faster than the speed of light. This was a pretty big deal because most of physics kinda relies on that one fact… but a couple of weeks ago, they said is was probably a problem with the electronics of the machine, that was giving the wrong speed. So physics was saved!
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