4
Parallax:
Really just the small angle formula
From the text, Horizons by
Seeds
The angular diameter here is “p” –
the “parallax” in arcsec.
The linear diameter is 1 AU.
d = 206265/p in AUs
d = 1/p in units of “parsecs”
1 parsec or 1pc = 206265 AU
1 pc = 3.26 light years