That's hilarious, I didn't even know a parsec was real. I always thought it was a word made up for Star Wars. That's why I used it, thinking it was fictional.
You could always say 16 by 9 and say the unit of measurement is a parsec :)
by the way, I usually say 16 to 9 or simply widescreen. The latter one usually works for my friends that don't really care.