Joseph Kittinger's Leap of Faith

Look carefully: You can just make out Air Force Colonel Joseph Kittinger, Jr. in a record-shattering free fall from the very edge of space on August 16, 1960, after jumping from a balloon-supported gondola 102,800 feet above New Mexico. During his descent, Kittinger reached approximate speeds of 614 miles an hour. The clouds beneath him are 15 miles away. Kittinger's leap was part of the Air Force's "Project Excelsior," which conducted research into high altitude bailouts from aircraft. Incredibly, almost 50 years later, Kittinger's record for the longest-ever free fall and highest parachute jump still stand.

Bruce McCandless' space ride

In February, 1984, astronaut Bruce McCandless floats 320 feet from the space shuttle Challenger during the first-ever untethered space walk, made possible by that most sci-fi of all gadgets, a jet-propelled backpack. Almost everything that makes the idea of exploring space can be found in this picture: the immediately recognizeable human form; the vastness of space; the blue glow of Earth, an impossibly long way off, and yet right there, in sight. For a second this picture feels comical. Quite quickly, it turns harrowing and thrilling at once.