One of my favorite misuse of the term, parsec, comes from the original Star Wars. Han Solo boasts about the SPEED of the Millennium Falcon in parsec…waa? LOL!
A parsec is an astronomical unit of distance derived by the theoretical annual parallax (or heliocentric parallax) of one arc second, and is found as the inverse of that measured parallax. Got it? No? The image above makes it a little easier to understand. In practical terms, one parsec equals about 3.26 light-years (30.9 trillion kilometres or 19.2 trillion miles).
The formula to calculate a parsec isn’t that hard (luckily most of the units cancel each other and you are left meters).
So why do we use parsec? Because until about 1964, the speed of light wasn’t really agreed upon, so no light-years until then, and scientists needed a way to make quick calculations of astronomical distances. Parsec is named from the abbreviation of the parallax of one arc
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