Parsec

(astronomy) The distance at which a star would have a parallax equal to 1 second of arc; 1 parsec equals 3.258 light-years or 3.08572 × 10¹³ kilometers. Derived from parallax-second.

A unit of measure of astronomical distances. One parsec is equivalent to 3.084 × 10¹³ kilometers, or 1.916 × 10¹³ miles. There are 3.26 light-years in 1 parsec. The parsec is defined as the distance at which the semimajor axis of Earth's orbit around the Sun (1 astronomical unit) subtends 1 second of arc. Thus, because the angle is small, the equation below holds. A parsec is then 206,265 astronomical units. At a distance of 1 parsec, the parallax is 1 second of arc. The nearest star is about 1.3 parsecs distant; the farthest known galaxy is several billion parsecs. See also Parallax (astronomy).