Parsec is a measure of distance from earth, not angular width.
OK. Thanks for clarifying that measurement. So if one is asking about the width of a nebula would it be measured in Light years or physical distance?
Here is what NASA says:
“Finally, parsecs. This is the unit used when the number of light years between objects climbs into the high thousands or millions. One parsec is 3.26 light years. The origin of this unit of measure is a little more complicated, but it’s related to how astronomers measure widths in the sky. Astronomers use “megaparsecs” — a megaparsec is 1 million parsecs — for intergalactic distances, or the scale of distances between the galaxies.”
https://solarsystem.nasa.gov/news/1230/cosmic-distances/