As objects become more distant, they appear smaller, because their visual angle decreases. The visual angle of an object is the angle subtended at the eye by a [[triangle]] with the object at its base. The greater the distance of the object from the eye, the greater is the height of this triangle, and the less the visual angle. This follows simply from [[Euclidean geometry]]. | As objects become more distant, they appear smaller, because their visual angle decreases. The visual angle of an object is the angle subtended at the eye by a [[triangle]] with the object at its base. The greater the distance of the object from the eye, the greater is the height of this triangle, and the less the visual angle. This follows simply from [[Euclidean geometry]]. |