I don’t understand it enough to explain it, actually I don’t really understand it myself at all
In: Physics
A parsec is a geometry thing. So easiest to see [using a diagram](https://en.wikipedia.org/wiki/File:Stellarparallax_parsec1.svg) or [two](https://en.wikipedia.org/wiki/File:Parsec_(1).svg).
If you take a right-angled triangle where one side is 1 AU (the average distance from the Earth to the Sun), and the opposite angle is 1 arcsecond (1/3600 of a degree or 1/1,296,000 of a whole circle), then the other side of the triangle will be 1 parsec long.
You can calculate the length using a bit of trigonometry if you’re comfortable with that.
Its use comes from the fact that as the Earth goes around the Sun distant stars appear to move in the sky, and by comparing their position when the Earth is on opposite sides of the Sun we can figure out how far away they are.
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