To test this prediction, Sir Arthur Eddington trekked to Africa in 1919 to observe the positions of stars seen near the sun during a total solar eclipse. As predicted, the stars appeared to shift ever so slightly from previously calculated positions, thus confirming Einstein's theory. Einstein quickly dismissed the possibility of ever observing such a phenomenon because it required an absolute perfect alignment of Earth, a massive star and an even more distant star. Not all astronomers gave up on the idea of finding these cosmic distortions, however. Still, it required major theoretical work in the 1960s, as well as instrument improvements in the 1970s, to set the stage for their discovery.
Quasars are the most energetic, distant objects known in the universe.
They also are fairly rare. Therefore, it seemed practically impossible that two identical quasars would appear right next to each other. Since then, astronomers have found more than 30 gravitational lens systems, some of which appear as rings and arcs, others as circles of beads and even one in the shape of a bull's-eye. Rather, they could help decipher some of the universe's greatest mysteries. For example, lenses can serve as cosmic yardsticks, helping astronomers determine how big and how old our universe is.