AAS #12: Einstein’s Double Bulls-eye

The picture above shows a cosmic bulls-eye of epic alignment. But before I can tell you about it, I have to tell you about how the dart got thrown. One of the more amazing aspects of looking into deep, deep space is that the path there is tortured and twisted. Space itself can be distorted by mass; it gets bent, like a road curves as it goes around a hill. And like a truck that must follow that road and steer around the hill, a photon must follow the curve of space. Imagine a distant galaxy, billions of light years away. It emits light in all directions. One particular photon happens to be emitted almost -- but not quite -- in our direction. Left on its own, we'd never see it because it would miss the Earth by thousands or millions of light years. But on its travels, it passes ...