Determining Tangential Peculiar Velocities of Clusters of Galaxies using   Gravitational Lensing
  We propose two new methods for measuring tangential peculiar velocities of rich clusters of galaxies. Our first method is based on weak gravitational lensing and takes advantage of the differing images of background galaxies caused by moving and stationary gravitational potentials. Our second method is based on measuring relative frequency shifts between multiple images of a single strongly lensed background galaxy. We illustrate this method using the example of galaxy cluster CL 0024+1654. 
S.M. Molnar (1), and M. Birkinshaw (2) ((1) Department of Physics and   Astronomy, Rutgers University, (2) Department of Phy...