Many animals, along with humans, have two eyes with overlapping visual fields that use parallax to gain depth perception this process is known as stereopsis. Parallax also affects optical instruments such as rifle scopes, binoculars, microscopes, and twin-lens reflex cameras that view objects from slightly different angles. These distances form the lowest rung of what is called 'the cosmic distance ladder', the first in a succession of methods by which astronomers determine the distances to celestial objects, serving as a basis for other distance measurements in astronomy forming the higher rungs of the ladder. Here, the term parallax is the semi-angle of inclination between two sight-lines to the star, as observed when Earth is on opposite sides of the Sun in its orbit. To measure large distances, such as the distance of a planet or a star from Earth, astronomers use the principle of parallax. Due to foreshortening, nearby objects show a larger parallax than farther objects when observed from different positions, so parallax can be used to determine distances. Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. In this case, the white cube in front appears to move faster than the green cube in the middle of the far background. As the viewpoint moves side to side, the objects in the distance appear to move more slowly than the objects close to the camera.

This animation is an example of parallax.

Parallax adjustment