#astronomy_unit__astronomyunit  a linear unit used for astronomical distances
  supertype:  linear_unit  a unit of measurement of length
  subtype:  light_year__lightyear  the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers
  subtype:  light_hour__lighthour  the distance light travels in a vacuum in one hour; approximately one billion kilometers
  subtype:  light_minute__lightminute  the distance light travels in a vacuum in one minute; approximately 18 million kilometers
  subtype:  light_second__lightsecond  the distance light travels in a vacuum in one second; approximately 300,000 kilometers
  subtype:  Astronomical_Unit__AU  a unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers)
  subtype:  parsec__secpar  a unit of astronomical length based on the distance from Earth at which stellar parallax is 1 second of arc; equivalent to 3.262 light years

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