If another background galaxy lies precisely on the same sightline, a second, larger ring will appear.

The massive foreground galaxy is almost perfectly aligned in the sky with two background galaxies at different distances.

Astronomers calculated that the background galaxy is 780 million light-years away.

This is possible because the gravity of the foreground cluster magnifies the light of the background galaxy.

The refraction indices of the wan light of distant background galaxies were wrong.

It was hardly more than a smear, apparently a tenuous obfuscation of background galaxies.

The observations, begun two years ago, relied on filtering to overcome the effects of foreground stars and background galaxies.

So, too, the background galaxies behind the ring show coherent changes in their shapes due to the presence of the dense ring.

The measurements of many background galaxies must be combined to average down this "shape noise".

Another interesting feature is the tenuous nature of the outer arms, through which a number of background galaxies can be seen.