Plain English Meaning

When you are moving, nearby things rush past quickly while distant things drift slowly. Your eyes use that difference in speed to tell what is close and what is far away.

Full Definition

A depth cue in which objects closer to the observer appear to move across the field of view faster than objects farther away when the observer is in motion. Pilots use this difference in apparent movement to judge the relative distance of terrain features, traffic, and obstacles.

Context Anchor

Seen in discussions of distance estimation, depth perception, and visual cues used while taxiing, landing, or judging height above the ground.

Derivation

From Latin movere ('to move') and Greek parallaxis ('' or 'change'). The term literally describes the change in apparent caused by motion, which is exactly how pilots use it to judge distance from a moving .