A
light year is the distance
light travels in one year, or more specifically, the distance that a
photon would travel, in free
space and infinitely far away from any gravitational
? or [magnetic field]
?s, in the time it takes the
Earth to complete on orbit of the
Sun. It is approximately equal to 9,500,000 million km (9.5 ×10
15 metres), because the
speed of light in a
vacuum is about 300,000 kilometers per second.
Note that the speed of light is used to measure large distances, like the distance from the solar system to nearest other star. A light year is not a unit of time. In astronomy, the parsec is nowadays the preferred unit for large distances; one parsec equals 3.26 light-years.
Interesting facts:
- It takes 8 minutes for light to travel from the Sun to the Earth.
- Our galaxy, the Milky Way, is 100,000 light years in diameter.
- No material object can travel faster than light. See Theory of relativity.
see also parsec, astronomical unit
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