What is a light-year?

The journal Nature recently published this letter announcing the exciting discovery of seven exoplanets 40 light-years away from Earth: only 235 trillion miles away! Does this mean it would take us 40 Earth years to reach those planets if we could travel as fast as the speed of light? The infographic below says light-years are a measure of distance, not a measure of time. Bonus question: Why can’t we travel faster than the speed of light, or can we?

Credit: niks1rocks, via SlideShare

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4 Responses to What is a light-year?

  1. CHC says:

    From Wikipedia: “The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/600th of a light-year in 30 years and is currently moving at 1/18,000th the speed of light. At this rate, a journey to Proxima Centauri would take 80,000 years.” Proxima C. is our closest star system.

    • Love Wikipedia … But what does it mean to say a light-year is a unit of distance and not a unit of time, since it takes X amount of time to travel Y distance?

      • Craig C says:

        Well, one can argue with the folks who named it a light-year I guess. But it is a distance. IF one could travel at the speed of light, THEN one could traverse this distance in a year. Otherwise, it would take longer, depending on one’s speed.

        I propose a new measure that combines distance and speed, called the light-bagel. It is defined by the seven feet that you are away from the front of the counter at Brugger’s Bagels, and all you want is one sesame and one everything, in a bag, to go, but you have to wait in line for all the people who want theirs toasted, with a smear of this or that, and so you are waiting in line, only seven feet away from talking to the uniformed minimum-wage bagel-prepper, for what seems like seven light-bagels, to place your simple order.

      • So close, yet so far …

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