An example of the parallax of an object against a distant background due to a change in location. When viewed from "Viewpoint A", the object appears to be in front of the blue square. When the viewpoint is changed to "Viewpoint B", the object appears to have moved in front of the red square.

Parallax is the perceived change in position of an object seen from two different places.

In astronomy, annual parallax is the only direct way to measure distance to stars outside the solar system.In essence, parallax is the perceived shifting phenomenon which occurs when an object is viewed from different positions.

It is measured by the angle between two lines of observation. Nearby objects have a larger parallax than more distant objects when observed from identical positions, so parallax can be used to determine distances.