1.   How gravitational lenses are to interpreted.

2.   Lesser radiations from galaxies and even single stars can also be seen through gravitational lenses.

3.   The degree and type of distortion of the image of a distant object also reveal information about the sometimes invisible gravitational lens in the foreground.

4.   These were gravitational lenses.

5.   Using the Hubble Space Telescope, the astronomers had pinpointed parts of the sky where potentially useful gravitational lenses exist.