Pan of the galaxy NGC 3370 taken by Hubble's Advanced Camera for Surveys in early 2003. Adam Riess, an astronomer at the Space Telescope Science Institute in Baltimore, Md., observed NGC 3370 a dozen times over the course of a month and has seen many Cepheid variables. These Cepheids are the most distant yet observed with Hubble. The total exposure time for this galaxy is extremely long (about one full day), and the combined image provides one of the deepest views taken by Hubble. As a result, thousands of distant galaxies in the background are easily discernable.