In order to view an object, you must sight along a line at that object. But in fact, you have to know that light will come from that object to your eye along this line of sight.
The object will only be seen if light reflected from that object penetrates the eye.
Learning objectives
To illustrate “a line of sight”, and zones of visibility.
How to use the animation
Click and drag the eye or the objects. Click and vertically drag the central obstacle.