Apollo 11 had 20 seconds of fuel left when it landed.

July 16, 1969: The world watched in anticipation as three men were hurtled skyward in a rocket bound for the moon.

Launched from Florida's Kennedy Space Center at 9:32 a.m. ET aboard a Saturn V rocket, Apollo 11 included a command module dubbed Columbia and a lunar lander called the Eagle.
 
The lander was named after the bald eagle in the mission insignia.

Apollo 11's journey to the moon took three and a half days. 

During that time the astronauts "just kind of gazed out the window at the Earth getting smaller and smaller, did housekeeping things, checking the spacecraft," Aldrin recalled.

As the craft passed through the shadow of the moon and started its approach, Aldrin and Armstrong got into the spider-like lunar module and began their descent.

The landing process didn't go flawlessly. Alarms sounded when the computer couldn't keep up with the data stream: "Nothing serious—it was distracting," Aldrin said.

"Neil didn't like what we were heading toward, and we selected a safer spot alongside a crater with boulders in it. We landed with a little less fuel than we would have liked to have had, maybe 20 seconds of fuel left."

Aldrin insists that he felt no real fear about landing on the moon.

Nevertheless, he said, "we kind of practiced liftoff [for] the first two hours. … We both felt that was the most prudent thing to do after touching down, was to prepare to depart if we had to."

Finally, with half a billion people watching on televisions across the world, the astronauts emerged from the Eagle to spend another two hours exploring the lunar surface.

The pair planted an American flag and placed mementos for fallen peers.

Armstrong uttered his famous first words, reportedly unscripted: "That's one small step for man, one giant leap for mankind."

Armstrong and Aldrin logged 21 hours on the moon—spending the last and longest portion of it trying to sleep in the frigid lander. Then they lifted off to rendezvous with Collins and Columbia for the return voyage.

The crew splashed down in the Pacific Ocean on July 24, 1969—and they were immediately put into a three-week quarantine.

As for their craft, the ascent stage of the Eagle was jettisoned into lunar orbit. Within a couple of years the lander smashed unseen into the moon. Columbia now sits on display at the National Air and Space Museum in Washington, D.C