This fundamental unit of interstellar distance is defined by trigonometry, representing the distance at which one astronomical unit subtends an angle of one arcsecond. It equals roughly 3.26 light-years or 30.9 trillion kilometres. Professional astronomers prefer it over light-years because it scales directly with observational parallax measurements taken from Earth orbit.
Heard on the job
The target star is located just under four parsecs from the solar system.
Insider tip
The name is a portmanteau of parallax and second.