astronomy math question

Question

if the parallax shift of a star is 0.150 seconds of sarc, what is the distance to the star in light years?

Answer 1

The distance r in parsec (pc) as a function of parallax p in arcsec is

 

r = 1/p = 1/(0.150 arcsec) ≅ 6.67 pc

 

1 parsec ≅ 3.26 light years (LY)

 

r = (6.67 pc)(3.26 LY/pc) ≅ 21.7 LY