Define parallactic second (parsec).

Explanation

Parsec is the distance when an arc of length equal to astronomical unit makes an angle of one second.
1 parsec `=(IA.U)/(1)` . Since, `1"=(1)/(3600)xx(pi)/(180)` rad
Therefore, 1 parsec `=(1.496xx10^(11))/((1)/(3600)xx(pi)/(180))=3.084xx10^(16)m`. Also 1 A.U.`=1.495xx10^(11)m`