Parsec

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A parsec is a unit of distance used in astronomy. It is the distance that light travels in 3.26 years, or just under 31 trillion kilometres (about 19 trillion miles).

Parsec
Stellarparallax parsec1.svg
A parsec is the distance from the Sun to an astronomical object which has a parallax angle of one arcsecond. (the diagram is not to scale).
Standard: astronomical units
Quantity: length
Symbol: pc
Expressed in: 1 pc =
SI units 3.0857×1016 m
imperial & US units 1.9174×1013 mi
other astronomical 2.0626×105 AU
   units 3.26156 ly

This is from the definition: a parsec is the distance from the Sun to an object which has a parallax angle of one arcsecond. The technique used in the calculation is trigonometry.

It takes 3.26 years for the light to come from a parsec away.