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.
Years ago, the boulder in the foreground broke loose and rolled on to this farm in northern Italy. Then this month, the boulder in the center of the photo tumbled down the mountain, tore through a barn and came to rest in a field. Fortunately, no one was hurt.
A tasseled wobbegong shark (top) lies on the seafloor with the head of a brown-banded bamboo shark in its mouth on the fringing reef of Great Keppel Island on Australia's Great Barrier Reef in August 2011.
Travelers at Pearson International Airport in Toronto earlier this month. At an unnamed airport, Canada's spy agency tested a program that allowed them to track those who took advantage of free Wi-Fi.
Aaron Harris /Reuters/Landov
Fireworks explode in a Shanghai street on Thursday, the eve of the Lunar New Year. Setting off firecrackers is meant to ward off evil spirits and bring good luck. But many Chinese say they won't buy firecrackers this year, owing to growing worries about air quality.
Peter Parks/AFP/Getty Images