An Etymological Dictionary of Astronomy and Astrophysics
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A unit of distance equal to 1,000 → parsec (pc)s, or 3,260 → light-years.

→ kilo-; → parsec.

A unit of distance equal to a million → parsec (pc)s, or 3.26 million → light-years.

→ mega-; → parsec.

A basic unit of astronomical distances, corresponding to a → trigonometric parallax of one second of arc. In other words, it is the distance at which one → astronomical unit (the mean radius of the Earth's orbit) subtends an angle of 1 arcsecond. 1 pc = 3.2616 → light-years = 206 265 astronomical units = 30.857 x 10¹² km.

From parallax + second.