The week's best photos
APTOPIX Space Shuttles Smithsonian
In this photo provided by the Smithsonian Institution via NASA, space shuttles Enterprise, left, and Discovery meet nose-to-nose at the beginning of a transfer ceremony at the Smithsonian's Steven F. Udvar-Hazy Center, Thursday, April 19, 2012, in Chantilly, Va. Space shuttle Discovery will take the place of Enterprise at the center to commemorate past achievements in space and retire as an artifact representing the 30-year shuttle program. (AP Photo/Smithsonian Institution via NASA, Carolyn Russo) MANDATORY CREDIT