• Question: How far is a lightyear ???

    Asked by gracerossiter to Aggelos, Andrew, Eileen, Naomi, Shane on 16 Nov 2012.
    • Photo: Andrew Jackson

      Andrew Jackson answered on 16 Nov 2012:


      It is the distance that like travels through a vacuum like space in one earth year. This is about 10 trillion kilometres – that’s 10 with eighteen zeros after it. By comparison, light from the moon takes only 1.2 seconds to reach earth. You might imagine how far it could go in a whole year!

    • Photo: Aggelos Zacharopoulos

      Aggelos Zacharopoulos answered on 16 Nov 2012:


      @gracerossiter, hi!
      One light year as Andrew says is the distance travelled by the light in one year.
      So if the speed of light is: 300,000 km/sec
      and one year has: 31,536,000 secs
      the light will travel around: 10,000,000,000,000 km in a single year!!!

      This is a lot!
      Think that. If you were an observer on earth and you see a beam of light arriving from a planet 10,000,000,000,000 away, that beam of light will show how that planet was a year ago!!!! This is one of the ways scientists use to look back in time when the Big Bang happened.

    • Photo: Eileen Diskin

      Eileen Diskin answered on 18 Nov 2012:


      This always confused me, since its called a ‘light year’ but it measures distance! (To me, a ‘year’ always just measured time). I think scientists decided to use this measure of distance because when we’re talking about how far away something is in outer space, things like miles and kilometers are just too small. Instead, it makes more sense to talk in terms of the speed of light, and how long it takes light to cover a certain distance.

      Because outer space is so big, and it takes light SO long to actually reach us on Earth…when we’re looking at a star, we’re actually seeing it as it was a long time ago!

Comments