The patterns seen here are called interference rings, or Newton’s rings, and are generated when light waves reflect off of two glass surfaces that are in very close proximity to each other, such as a glass microscope slide and a cover slip. Imperfections in the glass cause the waves to be reflected at different points of the wave. Where you see bright rings, two waves have been reflected “in phase” and an additive effect causes bright light to be seen. Where the rings are dark, the waves are reflected “out of phase” and cancel each other out, so no light is seen.
To see a diagram depicting this phenomenon and read more about interference rings, click here.
Artwork contributed by Don Pottle.