See also: lightyear and light-year

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Noun edit

light year (plural light years)

  1. (astronomy) A unit of length (abbreviation ly; equal to just under 10 trillion kilometres (1016 metres)) equal to the distance light travels in one Julian year; used to measure extremely large distances.
    • 2012 January, Robert L. Dorit, “Rereading Darwin”, in American Scientist[1], volume 100, number 1, archived from the original on 14 November 2012, page 23:
      We live our lives in three dimensions for our threescore and ten allotted years. Yet every branch of contemporary science, from statistics to cosmology, alludes to processes that operate on scales outside of human experience: the millisecond and the nanometer, the eon and the light-year.
  2. (only in plural, figurative, informal) A very long way.
    The marathon runner in the lead is light years ahead of the one at the back.
  3. (only in plural, figurative, informal) A very long time.
    Some of Leonardo da Vinci’s inventions were light years ahead of their time.

Usage notes edit

  • The light year is a unit of length, but because it contains the word year, it is sometimes assumed to be a unit of time. Its use in the figurative sense of "a very long time" is nonstandard; it is preferable to use an alternative term in this case.
  • light year and light-year are similarly common overall, lightyear lagging far behind.[1][2] light-year leads in the American corpus while light year leads in the British corpus.[1][2] GPO manual favors light-year.[3] Merriam-Webster has light-year.[4] OED has light year.[5]

Derived terms edit

Related terms edit

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References edit

  1. 1.0 1.1 light year, light-year, lightyear at Google Ngram Viewer
  2. 2.0 2.1 light years, light-years, lightyears at Google Ngram Viewer
  3. ^ 6. Compounding Rules in U.S. Government Printing Office Style Manual,
  4. ^ light-year”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.
  5. ^ light year”, in OED Online  , Oxford, Oxfordshire: Oxford University Press, launched 2000.

Further reading edit