Light Year

A Light Year is an length unit of measurement that is used informally to express astronomical distances.

• AKA: Light-Year.
• Context:
  • It is It is approximately 9 trillion Kilometres.
• Example(s):
  • a Cubic Light-Year.
  • …
• Counter-Example(s):
  • a Kilometer.
• See: Second of Arc, Astronomical System of Units.

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References

2016

• (Wikipedia, 2016) ⇒ https://en.wikipedia.org/wiki/Light-year Retrieved:2016-7-15.
  • A light-year (or light year, abbreviation: ly ) is a unit of length used informally to express astronomical distances. It is approximately 9 trillion kilometres (or about 6 trillion miles). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word year, the term light-year is sometimes misinterpreted as a unit of time.

    The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist and popular science publications. The unit usually used in professional astrometry is the parsec (symbol: pc, approximately 3.26 light-years; the distance at which one astronomical unit subtends an angle of one second of arc).

• http://www.astronomy.com/news/2016/07/more-than-1-million-galaxies-are-mapped-to-research-dark-energy
  • QUOTE: In the quest for dark energy, astronomers have created an unprecedented 3D map of 1.2 million galaxies in a volume of about 650 cubic billion light years.

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