During this activity, you saw how sight lines can be used to locate objects in space. Another useful technique for locating objects in space relies on something called parallactic motion. Parallax is the apparent change in relative position of near and far objects as one changes one s position of observation. For example, when you view objects while moving your head, you see the position of near objects change relative to far objects.
Parallactic motion provides another clue in locating objects in space.
This activity is designed to help you consciously use parallactic motion so that later you can skillfully locate the sources of light. You will soon be studying optical instruments like mirrors and lenses, and to understand how these instruments work, you need to be able to locate the source of light on which your eyes are focused. Since much of the light we use in life comes to our eyes via optical instruments, this is a fascinating topic to study. Figure 1 illustrates parallactic motion. The actual positions of the objects on the table have not changed but their apparent position relative to each other has changed because the position of the observed has changed.