You give astronomical distances beyond the solar system in light-years, but professional astronomy papers use parsecs. ... The parsec (which equals 3.26 light-years) is defined as the distance at which a star will show an annual parallax of one arcsecond.

Do astronomers use light years or parsecs?

The parsec is preferred by astronomers, whereas the light-year is more popular in science texts and everyday use.

Why do astronomers use parsecs?

Q: Why is a parsec 3.26 light-years and not some other number? A: A parsec, or “parallax second,” is defined as 3.26 light-years because of how it is measured. Earth circles the Sun, making one complete orbit per year.