A conceptional look at where the world ends and space begins. A tree lined horizon glows orange after sunset while Comet Pan-STARRS (C/2011 L4) and the crescent Moon (looks full because of Earthshine) shine in the twilight sky filled with stars. #conceptcollab
Boeing Model 307 Stratoliner - the first commercial transport aircraft with a pressurized cabin. This feature allowed the plane to cruise at an altitude of 20,000 ft (6,000 m), well above weather disturbances. Taken at the Steven F. Udvar-Hazy Center is the Smithsonian National Air and Space Museum at Washington Dulles International Airport.