Parallax's an apparent displacement or difference of orientation of an object viewed along two different lines of sight, and's measured by the angle or semi-angle of inclination between those two lines. The term's derived from the Greek παράλλαξις (parallaxis), meaning "alteration". Nearby objects have a larger parallax than more distant objects when observed from different positions, so parallax can be used to determine distances. In astronomy,… (More on Parallax)