Stellar Parallax

The heliocentric model of the Earth's revolution around the sun predicts a phenomenon called stellar parallax, the apparent shift of position of any nearby star (or other object) against the background of distant objects. Due to the annual motion of the earth around the Sun, the stars should change position slightly. It has been found that some stars exhibit zero parallax, while other stars exhibit positive or negative parallax of about equal distribution. Stars which exhibit negative parallax travel in a direction contradictory to heliocentrism, and are usually dismissed as "errors".

Negative Parallax
Reality Reviewed: Negative Parallax By Neville Thomas Jones, Ph.D. (bio) Full Link Text

Historical Quotes
"Negative parallax ...suggests that there is some unexplained source of error"

"Negative parallax renders uncertain all deductions from these observations"