Imagine holding a wine glass up to a candle (of course I had to pour a glass to try this.) The curved glass bends and distorts the flame, stretching it into arcs and rings of light. Now scale that up to the size of a galaxy, replace the glass with a trillion solar masses of matter, and the candle with an entire galaxy billions of light years away. What you get is one of the most beautiful and scientifically powerful phenomena in all of astronomy, a gravitational lens. Einstein's general theory of relativity tells us that mass warps the fabric of space itself. Light, following that curved space, bends around massive objects like galaxies and galaxy clusters. When the alignment is just right, the result is extraordinary, background galaxies appear stretched into glowing arcs, or smeared into perfect rings known as Einstein rings. These are not tricks of the eye. They are the universe bending light around corners.…