George Washington leads his troops across the Delaware River in 1776 during the Revolutionary War in this painting by Emanuel Leutze. AP hide caption

Researchers Evgenia Ilyinskaya and Asgerdur Sigurdardottir sweep up volcanic ash from a small bridge just south of the Eyjafjallajokull volcano. The ash will be taken back to the University of Iceland for analysis. Joe Palca/NPR hide caption

The MODIS instrument on NASA's Terra satellite captured an ash plume from the Eyjafjallajokull volcano on Friday. Though satellite images can tell scientists where the ash is, they don't help forecasters determine how much ash is in the air — or at what point it becomes a hazard to airplanes. MODIS Rapid Response Team/NASA via Getty Images hide caption

Researchers say it's not just loose skin that makes us look old; it's our bones. These skulls from the Smithsonian Museum of Natural History show the loss of definition in the lower face. Nate Lavey/NPR hide caption

Pope Benedict XVI waves from the popemobile during his weekly general audience, in St. Peter's Square at the Vatican. Pier Paolo Cito/AP hide caption