parallax second /(?)/

par·al·lax sec·ond

parallax second

n.
  1. An annual parallax of one second of an arc; -- applied to celestial objects outside the solar system. It is used to measure the distance of an astronomical object from the Earth. A star which has an annual parallax of one second of an arc is considered to be one parsec (3.26 light years) distant from the earth. See parsec in the vocabulary.