If the retinal image increases in size, the object is moving:

If the retinal image increases in size, the object is moving:

• A. The object is moving away
• B. The object is moving closer
• C. The distance is constant
• D. The retinal image is decreasing in size

Answer: (B)

When an object gets closer, it subtends a larger angle on the retina, so the image on the retina increases in size. The retinal image size is roughly proportional to the object's angular size, which is about the object's real size divided by its distance for small angles. Therefore, if the retinal image is growing, the distance to the object is decreasing and the object is moving toward you. If it were moving away, the retinal image would shrink; a constant distance would keep the image size the same.

When an object gets closer, it subtends a larger angle on the retina, so the image on the retina increases in size. The retinal image size is roughly proportional to the object's angular size, which is about the object's real size divided by its distance for small angles. Therefore, if the retinal image is growing, the distance to the object is decreasing and the object is moving toward you. If it were moving away, the retinal image would shrink; a constant distance would keep the image size the same.