Difference between revisions of "Speed of light"
(RV: I think a explanation consistent with Genesis is appropriate but will defer if sufficient users think otherwise) |
Tmtoulouse (talk | contribs) (If its between sticking Genesis EVERYWHERE and just not dealing with "age" issues I say we ignore the ramifcations on age) |
||
| Line 3: | Line 3: | ||
The speed of light is slower in any medium which is not a vacuum, and varies from medium to medium. This variation gives rise to (as a result of [[quantum mechanics]], particularly the concept of a path of least action) the phenomenon of [[refraction]]. | The speed of light is slower in any medium which is not a vacuum, and varies from medium to medium. This variation gives rise to (as a result of [[quantum mechanics]], particularly the concept of a path of least action) the phenomenon of [[refraction]]. | ||
| − | Since the speed of light in a vacuum is constant, it can be used to define distances as well. The distance that light travels in one year is know as a [[light-year]], which is about 6 million million (6x10^12) miles. For instance, the nearest large galaxy to our own [[Milky Way Galaxy]] is the [[Andromeda Galaxy]], which astronomers have measured to be about 2.5 million light years away | + | Since the speed of light in a vacuum is constant, it can be used to define distances as well. The distance that light travels in one year is know as a [[light-year]], which is about 6 million million (6x10^12) miles. For instance, the nearest large galaxy to our own [[Milky Way Galaxy]] is the [[Andromeda Galaxy]], which astronomers have measured to be about 2.5 million light years away. |
Revision as of 20:08, March 8, 2007
The speed of light in a vacuum (which is constant for all observers: see the theory of relativity) is, to nine significant figures, exactly 299,792,458 metres per second (approximately 1,079,252,848 km/h). As the speed of light is used to define the SI metre, this is the value by definition.
The speed of light is slower in any medium which is not a vacuum, and varies from medium to medium. This variation gives rise to (as a result of quantum mechanics, particularly the concept of a path of least action) the phenomenon of refraction.
Since the speed of light in a vacuum is constant, it can be used to define distances as well. The distance that light travels in one year is know as a light-year, which is about 6 million million (6x10^12) miles. For instance, the nearest large galaxy to our own Milky Way Galaxy is the Andromeda Galaxy, which astronomers have measured to be about 2.5 million light years away.