An Einstein Cross

Or, gravitational lensing. It is when a distant object in space has so much gravity that it bends light around it allowing for us to observe what is behind the object. Blackholes, quasars and galaxies being the primary sources of gravitational lensing.

Sometimes this effect helps us to see distant objects even clearer because it magnifies that which is behind it. Recently astronomers were able to see a supernova replay over and over as this light reached us from the same event many times over several years. Weird.

Here is a fairly good explanation:

The New York Times has more.