NASA has released an animation commemorating the 45th anniversary of Apollo 8, the first manned mission to orbit the moon. The famous "Earthrise" photo was taken on Christmas Eve 1968.

"It really came about by accident," space author Andrew Chaikin, who narrates the video, tells NPR's Morning Edition in an interview that will air Tuesday.

Comparing new data from the Lunar Reconnaissance Orbiter probe, which has been circling the moon since 2009, with the Apollo 8 astronauts' photography and Apollo 8's onboard audio, theGoddard Space Flight Center's Scientific Visualization Studio has been able to discover just how serendipitous the famous snapshot was.

"It turns out that the only reason the astronauts saw the Earth when they did was because Frank Borman, the mission commander, was in the process of rotating the spacecraft — which was pointing nose down at the moon," Chaikin tells NPR.