one of my favorite silly sci-fi tropes is the use of parsecs as a unit of measuring distance by people who are engaging in faster-than-light interstellar travel. parsecs make no sense to anyone outside the context of astronomy and you just know that any engineer having to work with them in the context of "yeah we do about 12 parsecs to a milligram of dilithium on this baby" would hate it intensely.
A parsec, if you're unfamiliar, is a unit of measurement used by astronomers because it relates directly to the way they make observations. To measure how far away a distant star or galaxy is, you make an observation of it, then make another observation six months later (when the earth is on the opposite side of the sun) and compare the angles. You then do some trigonometry and figure out how far away it is. A parsec is the distance given by one arcsecond (1/21600 of a full circle) over one astronomical unit (the distance between Earth and the Sun).
The parsec has several benefits to astronomers. First, it doesn't cleanly convert to any other unit. It's about 3.26 light-years, 206kAU, or 30.9 trillion kilometers. Now, a natural unit, like the light-year, is nice because it relates two natural quantities (the speed of light in a vacuum and the length of the solar year) to each other and thus is very clearly defined. Parsecs are not that because they're based on splitting circles into 360 degrees, then 60 arcminutes to a degree, then 60 arcseconds to a minute. The astronomers were truly cooking on this one; radians are right there, a way of defining angles without reference to arbitrary subdivisions of the circle. But that wouldn't have been arcane enough, so arcseconds it is.
The parsec, I'm pretty convinced, is a generational long con on the part of astronomy as a research field. The astronomers know that if interstellar travel ever becomes a reality, their bullshit will heavily influence how it is measured and planned but they're not the ones who will have to do the math. The purpose of it seems to be to make sure that hypothetical future starship drive engineers will suffer the same constant agony that afflicts present-day programmers who have to deal with times and dates (another long-term torture project perpetrated by astronomers).
