Bobbie Hanvey and his son Steafán Hanvey, in Northern Ireland. Courtesy of Peter Muhly hide caption

itoggle caption Courtesy of Peter Muhly

A couple taking in the moment at the San Tan Valley Desert in Arizona. Tammy Watson hide caption

itoggle caption Tammy Watson

Wellington Costa, 19, performs at the semifinals of a passinho competition in Rio de Janeiro on April 23. Passinho is a liberated dance form born in Rio's favelas, or shanty towns. Lianne Milton for NPR hide caption

itoggle caption Lianne Milton for NPR

East Boston, Mass., in 1973 (left) and in 2012. Michael P. Manheim/Environmental Protection Agency hide caption

itoggle caption Michael P. Manheim/Environmental Protection Agency

Nanoflowers, each smaller than the thickness of a dollar bill, sprout up spontaneously on a surface dipped in salts and silicon. Courtesy of Wim Noorduin/Harvard University hide caption

itoggle caption Courtesy of Wim Noorduin/Harvard University

Sonny Vaahn, 25, holds his family's refugee identification in Bronx, N.Y. The card was issued to them during their initial entry into a refugee camp along the Thai-Cambodian border after the "killing fields" atrocities ended in Cambodia. Courtesy of Pete Pin hide caption

itoggle caption Courtesy of Pete Pin