The apparent motion of an object
due to the observer’s motion.
Nearby stars show an annual
parallax, But the magnitude of the
motion is exceedingly small due to
the great distances to even the
nearest stars.
parallax
(contraction of parallax-second)
A unit of distance in astronomy. A
star one parsec away would seem
to shift back and forth by one
second of arc as we orbit our Sun
each year.
parsec
the point of closest approach of an
object orbiting the Earth in an
elliptical orbit.
perigee
The point in a planet’s orbit
around the Sun where that
planet is closest to the Sun.
It’s orbital speed is greatest
here.
that alignment of a planet
where it is seen precisely ninety
degrees on either side of the
Sun. It does not have much
physical significance, but is of
interest when planning an
observation of the object.
quadrature
