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 arcsecond, around 1913 by British astronomer Herbert Hall Turner. It is also a little easier for the average person to figure out how much distance light travels in a year verse doing some trigonometry.  Today, depending on the field, light years are probably used more than parsecs, but they both have their place in science.

– Ex astris, scientia –

I am and avid amateur astronomer and intellectual property attorney in Pasadena, California and I am a Rising Star as rated by Super Lawyers Magazine.  As a former Chief Petty Officer in the U.S. Navy, I am a proud member of the Armed Service Committee of the Los Angeles County Bar Association working to aid all active duty and veterans in our communities. Connect with me on Google +

Norman