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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).
General information
Unit system astronomical units
Unit of length
Symbol pc 
Conversions
1 pc in ... ... is equal to ...
   SI units    3.0857×1016 m
   imperial & US units    1.9174×1013 mi
   other astronomical    2.0626×105 AU
      units    3.26156 ly

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). This is from the definition: a parsec is the distance from the Sun to an object which has a parallax angle of one arcsecond.

Distances measured in fractions of a parsec usually involve objects within the same star system.

Surveying provides an everyday example of parallax. Go outside and look at a distant object. Hold your hand out with one finger raised and close one eye. Line up your finger so it covers the object from view. Then close that eye and open the other without moving your arm. Now, move your finger to block that eye's line of sight. The two positions your finger was at can be used to find the distance from the object. This is what a survey crew does to figure out land plot boundaries. The mathematical technique used in the calculation is trigonometry. A parsec is so large that if you could see that far that you would be looking in to the past. You are looking 3.26 years in the past because it takes 3.26 years for the light to come from a parsec away.

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See also

Kids robot.svg In Spanish: Pársec para niños

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