Parallax

parallax

noun [par-uh-laks]

1. the apparent displacement of an observed object due to a change in the position of the observer.
2. Astronomy. the apparent angular displacement of a celestial body due to its being observed from the surface instead of from the center of the earth (diurnal parallax or geocentric parallax) or due to its being observed from the earth instead of from the sun (annual parallax or heliocentric parallax). Compare parallactic ellipse.