the Earth at great speed, which meant they must be very far away. And yet, for quasars to appear as bright as they do and to be so far away, they must produce prodigious energy—so much energy, in fact, that some astronomers suggested they really were not so far away, and therefore were not so energetic, after all. In this case, however, we know the distance of the gravitational “lens” (the galaxy). We also know the lens only affects objects behind it. Thus gravitational lensing demonstrates that quasars really are at great distance—and just as inexplicably energetic as they were originally thought to be.
    Finally, gravitational lensing solves an important puzzle about