Mathematical models of the mass distribution of a galaxy cluster provide magnification maps that pinpoint the locations of greatest magnification due to gravitational lensing. These are where astronomers search for the most distant and faintest galaxies. Shown here are Hubble imagery of galaxy cluster Abell 2744 (green); distribution of mass for the Abell 2744 galaxy cluster (blue); and locations of greatest lensing for background galaxies with a redshift of 9 (pink). There are different magnification maps for background galaxies at different distances. Credit: J. Richard (CRAL Lyon), CATS team, and D. Coe (STScI)