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by JP1967 on January 7th, 2004

JP1967

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How far is a light-year? In miles and kilometers.

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Answers. 18 helpful answers below.

  • by Relsqui on March 17th, 2006

    Relsqui

    Great Answer

    Hand-picked by Answerbag's staff. (What's this?)

    A light year is a unit of distance (not time!) equal to the speed of light in a vacuum times the duration of one Julian year--in other words, how far light could travel in a vacuum in a year, assuming no influence by gravitational or magnetic fields. It's used, mostly by laypeople, to discuss the differences in stars. (Professionals prefer the parsec.)

    So how far is that? Exactly 9,460,528,410,545,436.2688 meters, and when I say "exactly" I mean it--the meter is defined relative to the speed of light in a vacuum (specifically, as the distance it can travel in 1/299,792,458 of a second), and as the number of seconds in a year is a fixed constant, you can't get more precise than that. You can express the same value slightly less precisely, though, as 5,878,625,373,184 miles.

    For what it's worth, a light year is also about 63,241.077 astronomical units, which are the defined as the average distance between the earth and the sun. That's even less precise than the above, though, seeing as the currently accepted length of one AU comes with a 30-meter margin of error.

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  • by wickedwillie on January 7th, 2004

    wickedwillie

    One light year is 186,000 X 60 X 60 X 24 X 365 miles. Light travels 186,000 miles per second, and there are 60 seconds in a minute; 60 minutes in an hour; 24 hours in a day; and 365 days in a year. That's a total of 5,865,696,000,000 miles, which is in kilometers multiplied by 1.60934 = 9,439,899,200,640 km...

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  • by Stepper on June 24th, 2009

    Stepper

    A light year is the distance that a beam of light travels over the course of one calendar year.

    It is equal to about 5,865,696,000,000 miles.

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  • by Anonymous on June 6th, 2009

    Anonymous

    a light year is 5,874,601,673,544 miles as the spead of light is 670,616,629.4 mph or 186,282 miles per second so 670,616,629.4 X 24 X 365 = 5,874,601,673,544 miles per year or 9,454,231,457,301.3 km

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  • by just wondering on October 24th, 2008

    just wondering

    so how far in miles was the star trek voyager from earth?

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  • by woodturner on November 23rd, 2005

    woodturner

    Not to be too picky but in 2004 it was a little further than the regular answer - that was a leap yr

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  • by dan daffron on August 7th, 2004

    dan daffron

    The formula listed works and is correct, but who can remember let alone translate all of those digits. For conversational purposes 6 trillion miles works for me!

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  • by Anonymous on June 6th, 2009

    Anonymous

    a light year is 5,874,601,673,544 miles as the spead of light is 670,616,629.4 mph or 186,282 miles per second so 670,616,629.4 X 24 X 365 = 5,874,601,673,544 per year

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  • by CaRbOnPrOdUcK is Baccuss on October 2nd, 2008

    CaRbOnPrOdUcK is Baccuss

    The distance that light travels in a vacuum in one year, approximately 9.46 trillion (9.46 × 1012) kilometers or 5.88 trillion (5.88 × 1012) miles.

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  • by Anonymous on January 14th, 2008

    Anonymous

    In kilometers I got (in standard form using 3.0*10^5 km/s)

    1 year= 31,556,926 seconds.

    Distance = Speed*Time
    Distance = 300,000*31,556,926
    Distance = 9.4670778*10^12 km/s

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  • by swalton1 on January 27th, 2012

    swalton1

    520 light year away, what is the distance to this star in kilometer

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  • by ggrlads on January 3rd, 2011

    ggrlads

    A lightyear is used to measure the distnaces between objects in space that are too great for the common measurements we use here such as kilometers and miles. A lightyear measures the distance light can travel in one year. Light travels at around 300,000 kilometers or 186,400 miles per second. In a year it is about 10 trillion kilometers of 5,850,000,000,000 miles.

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  • by MaxPro on August 28th, 2010

    MaxPro

    This is easy to work out for yourself if you know the speed of light.


    186,000 miles per second

    x60 = per minute
    x60 = per hour
    x24 = per day
    x365 = per year

    Not far off 6 trillion miles as stated.

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  • by Midnightagic on April 2nd, 2004

    Midnightagic

    Actually, a light year is 15 Earth years. So I guess your equation should be multiplied by 15.

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  • by Dimitrios Kousoulas on November 28th, 2005

    Dimitrios Kousoulas

    A spaceship traveling at half the speed of light (2,932,848,000,000 miles per Earth year) will take approximately nine Earth years to come to Earth from a planet in Alpha
    Century (the nearest solar system).
    A spaceship traveling from the Earth to a planet in Alpha Century at ten times the speed of our current NASA spacecraft (40,000 x 10=400,000 miles per hour) will take 7,500 Earth years to reach its destination.

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  • by Canepohl on December 17th, 2009

    Canepohl

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  • by MPax4059 on June 15th, 2006

    MPax4059

    In miles, it would be 5,865,696,000,000
    OR

    fife trillion, eight-hundred sixty-five billion, six-hundred ninety-six million miles.

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  • by Anonymous on October 1st, 2008

    Anonymous

    I found that one year is 365 days, 5 hours, 46 mins, 48 secs. If light travels at 299,972,458 metres/second, that equates to 186,291.0334 miles/second. 365d,5h,46m,48s, works out at 31,556,926 seconds. multiply them and 1 light year equals 5,878,772,355,467.3284 miles. i think!!

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