On Sept. 18, 1977, NASA's Voyager 1 spacecraft took a photo of Earth and the moon.

It was the first time both the Earth and the moon were captured in a single frame. At the time, Voyager 1 was more than 7 million miles away from Earth. It had launched about two weeks earlier on a mission to explore the outer planets. Voyager 1 passed through the asteroid belt and visited Jupiter and Saturn. Then it took a sharp turn and started heading straight out of the plane of the solar system. Before Voyager 1 went into interstellar space, Carl Sagan convinced NASA to turn its cameras around one last time to take a family portrait of all the planets in the solar system. This family portrait shows Earth as a tiny speck in a ray of sunshine. It is now famously known as the "Pale Blue Dot."