• Question: What is ment by the term "light years"

    Asked by Oliver Johns to Heather, Helen, Hugh, Jane, Julian on 17 Nov 2014.
    • Photo: Julian Onions

      Julian Onions answered on 17 Nov 2014:

      A light year is a measurement of distance.
      Because distances in astronomy are so huge, we can’t really deal in metres or kilometers, there are just too many of them.
      So we use a new unit to make these distances easy to talk about.
      The light year is the distance light travels in one year. As it travels at a speed of 186,000 miles/second, or about 3,000,000 km/s
      So a light year is about 9,460,730,472,580,800 metres.
      The nearest star is about 4 light years away, the galaxy is probably about 100,000 light years across and the nearest galaxy about 2.5 million light years away.

      So although it sounds like a unit of time, its a unit of distance.

      Most professional astronomers tend to use the parsec as a unit though, with about 3 light years to a parsec.

    • Photo: Helen Johnson

      Helen Johnson answered on 17 Nov 2014:

      If you’re a Star Wars fan, this quote always gets scientists confused…
      “You’ve never heard of the Millennium Falcon?… It’s the ship that made the Kessel Run in less than twelve parsecs.”

      They talk about a parsec like it’s a time unit when actually, as Julian said, it’s a distance!

    • Photo: Heather Campbell

      Heather Campbell answered on 17 Nov 2014:

      Light years means the distance that can be traveled by light (or anything traveling at the speed of light, 300,000,000 m per s) in one year. The distance light can travel in one year is equal to 9500000000000 km (9.5×10^12 km)!

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