parallax second \par"al*lax sec"ond\, n.
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.
[PJC]