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    #1

    light year

    what does "light" mean when we say "light year" ?
    (I think it means "happy" am I right ?)

  1. BobK's Avatar
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    #2

    Re: light year

    Quote Originally Posted by ehsanshekari View Post
    what does "light" mean when we say "light year" ?
    (I think it means "happy" am I right ?)
    It means the distance traveled by light in a year. So it's an extent of space rather than an extent of time (although if you accept the view that spacetime is a single dimension, that sentence doesn't make a lot of sense - although trying to align theoretical physics with 'common sense' tends not to make much sense anyway)

    Modern astronomers usually prefer to use the expression "parsec" ("parallax of one second of arc") - Parsec - Wikipedia, the free encyclopedia. As that article says,
    Articles aimed at a wider audience, such as in newspapers and popular science magazines, often use a more intuitive unit, the light-year (ly).
    b

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    #3

    Re: light year

    I always thought I'm a clever boy , but your answer taught me that my IQ is under average .
    (I understood the meaning of light year but I couldn't understand the other sentences.My English is too weak.)
    Thanks
    Ehsan Shekari

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