Spherical Reflections
To do and notice:
Look at the spherical mirrors from various angles. Notice that the image in each mirror is a little different from the image in the neighboring mirrors. That's because each mirror "sees" the world from a slightly different vantage point. Notice that if you point your finger at one sphere, the image of your finger in all the other mirrors will point at the chosen mirror.
The dark sections between the balls occur because all the light is reflected back and forth between the balls, and none of it gets to the eye. The exhibit’s plexi-glass door can be raised to reveal that the balls are in fact round, even though the dark edges make them appear to be crinkled. Also notice that your image is very small in the mirrors, and that it appears quite far away.
What’s going on?
Each Christmas tree ball is a convex mirror - a mirror that curves out toward the source of light. Convex mirrors reflect images that are smaller than life-sized. In the ray diagram below, notice the reflection of three rays of light from a particular point at the tip of the pencil. Your eye and brain follow these reflected rays backward along a straight line to their apparent intersection behind the mirror. All other reflected rays from the point also seem to originate at this intersection. The reflected rays from all other points on the pencil also appear to intersect at specific points behind the mirror. All these intersection points put together create what's called a virtual image.
The Purpose:
Convex rearview car mirrors have a written warning cautioning that objects are actually closer than they appear. Your brain assumes that when an object that is known to be large - a car, for instance - has a small image in a mirror then the object is far away. In a convex mirror, however, an image that appears quite small can actually be very close. Also, convex mirrors are often used as security mirrors in stores, since they reveal a broad field of view.