Feature

Reflections in Christmas Tree Balls

Douglas S. Goodman

Many optical phenomena can be seen and many beautiful effects can be produced with Christmas tree ornaments. The kind to use is the plain silver balls, the bigger the better. The main optical property involved here is that a sphere reflects light from all directions into any given direction or to any point. Thus, an eye looking at a sphere sees in all directions, as shown in the figure. (We can also think of the sphere as forming an image of all that surrounds it. The image is contained within the sphere, and is seen when the eye lens re-images it onto the retina.)