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Parsec: 3.26 light years = 19.2 trillion miles. A parsec is defined as the distance to a body with a heliocentric parallax of one second, hence "par - sec" = parallactic second.
Estimated to contain 10 to the 11th stars, The Galaxy is a disc-like structure with a diameter of some 30,000 parsecs, a central elllipsoidal nucleus of about 4000 parsecs, and an average disc thickness of several hundred parsecs.
space where the Sun's solar wind runs into the solar winds of the stars (the heliopause), is 100 AU from the Sun. Comets in highly elliptical orbits can travel as far as 50,000 AU from the Sun. For larger distances, light years or parsecs are used.
 See also: Symbol, Horizon, Part, House, Houses
  
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