Sean Morey, then with the Arizona Cardinals, celebrates after blocking a punt against the Seattle Seahawks in 2007. Morey, who suffers from post-concussion syndrome, retired from the NFL in 2010 on the advice of doctors. Stephen Dunn/Getty Images hide caption

itoggle caption Stephen Dunn/Getty Images

Janet Yellen smiles as President Obama announces her nomination for Federal Reserve chairwoman on Oct. 9. Jewel Samad/AFP/Getty Images hide caption

itoggle caption Jewel Samad/AFP/Getty Images

Cannonball jellyfish soak up the sun on a South Carolina beach. Fishermen are now pursuing the pest that used to clog their shrimping nets. Courtesy of Steven Giese hide caption

itoggle caption Courtesy of Steven Giese

Linda Door protested outside the U.S. Supreme Court as it began hearing arguments on the constitutionality of the Affordable Care Act in March 2012. Carolyn Kaster/AP hide caption

itoggle caption Carolyn Kaster/AP

A protest of the Keystone XL pipeline last March along its proposed route near Bradshaw, Nebraska. NH/AP hide caption

itoggle caption NH/AP

Gund Kwok troupe member Heang Ly takes a break next to her lion costume during a rehearsal in Boston's Chinatown. Hansi Lo Wang/NPR hide caption

itoggle caption Hansi Lo Wang/NPR

Andrew Ng and Daphne Koller, Stanford University computer science professors who started Coursera, pose for a photo at the Coursera office in Mountain View, Calif., on Aug. 2, 2012. Jeff Chiu/AP hide caption

itoggle caption Jeff Chiu/AP

Dark blue: It's going to take a foot or more of snow to close schools. Green: Any snow's going to shut things down. reddit.com/user/atrubetskoy hide caption

itoggle caption reddit.com/user/atrubetskoy