Light year

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.

The speed of light in a vacuum, denoted by c, is equal to 299,792,458 metres 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.

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