The Apollo program transfixed the United States and the world in the 1960s for its heroic effort to fulfill the promise of President John F. Kennedy to go to the moon. But its most endearing legacy may have been, not visiting the barren world that is our planetary companion, but granting us a view of the bounteous world that is our home.

When Apollo 8 astronaut William Anders snapped a photograph of Earth, partially in shadow, rising above the moon’s surface in 1968, he provided the clearest image yet seen of our world and its fragility in space.

'Earthrise,' 'Blue Marble' and 'Pale Blue Dot' 

The Apollo missions, which concluded in 1972, coincided with the birth of the modern environmental movement—the founding of Friends of the Earth in 1969 and Greenpeace in 1971, the first Earth Day in 1970, among other seminal events—and the sight of Earth from space offered inspiration and motivation. Many years later, photographer Galen Rowell described Earthrise as “the most influential environmental photograph ever taken.”

Earthrise was followed by Blue Marble, a view of the Earth taken from the Apollo 17 spacecraft in 1972. That was the last of the Apollo moon missions, but NASA’s space probes continued to take longing glances back toward their home world. 

WATCH: How the Earth Was Made on HISTORY Vault.

Among the most famous of those images was taken in 1990. On the initiative of Carl Sagan, who first proposed photographing Earth with Voyager cameras in 1981, Voyager 1 snapped the image of a barely visible Earth that became known as the “Pale Blue Dot.” Voyager also captured images of Neptune, Uranus, Saturn, Jupiter and Venus, and staff at NASA’s Jet Propulsion Laboratory mounted the set as a mosaic on an auditorium wall. The image of Earth had to be repeatedly replaced because so many people touched it.

A Library of Earth Images Continues to Grow

In 1989, NASA formalized a Mission to Planet Earth, in which examining the third planet from the sun was no longer incidental to its work but central to it. In the three decades since then, the agency’s Earth Science program observation has expanded along with both the technological ability and the growing imperative to do so.

Through interplanetary probes, orbiting satellites and camera-wielding astronauts on space shuttles and the and the International Space Station, NASA and partners such as the European Space Agency (ESA) have compiled an ever-growing image library of our own planet. 

The images reveal how Earth is altered by land use, human activities, weather phenomena and climate changes. The thousands upon thousands of images reveal moments in time and seemingly timeless vistas, of our world up close and from afar.

As Anders himself observed, 50 years after his first Earthrise image was released: “We set out to explore the moon, and instead discovered the Earth.”