Why do astronomers use irregular units like "light years" and "parsecs"
I can't remember the last time I read an astronomy paper (NB : paper, not regurgitated shit in the popular press) which didn't use parsecs and/or AU as the primary description of astronomical distance (with , M-Earth and M-Sol in the mix). For parsecs, the reason is simple : what you measure when establishing distances is parallax, in seconds of arc. Hence PAR-SEC. No?
If converting to metres, then you need to factor in your estimate for the AU, but you only do that conversion when editing the final draft of the paper and the press release You do your working in parsecs. And if the estimate for the length of the AU in metres changes between your observatory time and publication date, then only that derived figure in metres (miles, Egyptian cubits, or whatever) changes NONE of your working or your experimental data changes.
Similar arguments apply to the masses and the AU. You can directly observe e.g. the timing of events in an eclipsing binary (in seconds or days after the start of your epoch of observation), and if you work in units of AU, M-Sol and M-Earth then you get your orbital parameters from those raw observations and Kepler's laws with no conversion factors. You only do the conversions for the proof copy of the paper - possibly not even for the initial copy to go to peer review.