Video: Astronauts mark 50 years in orbit

Do human eyeballs change shape in space? That was just one of the questions former astronaut John Glenn sought to answer 50 years ago when he became the first American to orbit Earth. Glenn and former astronaut Scott Carpenter attended a ceremony at NASA's Kennedy Space Center marking the 50th anniversary of Glenn's flight aboard the Friendship 7 spacecraft on Feb. 20, 1962.

The two astronauts, along with NASA administrator Charles Bolden, spoke live to the astronauts currently orbiting Earth aboard the International Space Station.

Glenn will give a keynote address on March 2 as part of a tweet-up at the Glenn Research Center in Cleveland.