On July 20, 1969, Apollo 11 landed on the moon and Neil Armstrong took one giant leap to become the first human to walk on it.

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Putting a man on the moon was a national goal set by President John F. Kennedy on May 25, 1961.

In his post-flight press conference, Armstrong called the historic mission -- by more than a half-billion people -- "a beginning of a new age."

Here are 11 interesting facts about the Apollo 11 moon landing:

1. There were three crew members.

The Apollo 11 crew included Armstrong as commander, Edwin E. (Buzz) Aldrin Jr. as Lunar Module pilot and Michael Collins as Command Module pilot.

2. The astronauts almost didn’t stick the moon landing.

The astronauts missed the initial landing site and were headed toward a crater. With less than one minute of descent fuel left, Armstrong piloted the Lunar Module 4 miles from the original landing site, according to National Geographic.

3. What were the first words spoken on the moon?

It's debatable. If you count the moment The Eagle touched down on the moon's surface, Aldrin's first words were "contact light."

But, according to NASA chief historian Bill Barry, if you're talking about the first words spoken the moment humans stepped onto the surface, the first words would be Armstrong's famous statement, "That's one small step for man, one giant leap for mankind."

4. The famous “one small step for man, one giant leap for mankind” phrase isn’t exactly what Armstrong said he said (or intended to say).

According to CNET, Armstrong may have messed up his famous phrase, which was supposed to be "one step for a man, one giant leap for mankind" (with the inclusion of an "a" before "man.")

In his 2006 biography, Armstrong said he did actually say the “a” and people just didn’t hear it.

“I think that reasonable people will realize that I didn't intentionally make an inane statement and that certainly the 'a' was intended, because that's the only way the statement makes any sense,” he wrote.

5. And that “one small step” wasn’t actually so small.

Armstrong actually had to hop about 3.5 feet from the Lunar Module‘s ladder to reach the surface.

6. The flag placed on the moon was made by Sears (and was knocked down as soon as the crew launched back into orbit).

In a July 3, 1969, NASA press release, NASA said the flags bought for the mission were purchased by different manufacturers in the Houston, Texas, area, but eventually it was discovered they were all bought at Sears.

NASA didn't want to confirm the manufacturer because it didn't "want another Tang" (or inclusion in any advertising campaign).

The flag placed on the surface of the moon was knocked over when Aldrin and Armstrong launched the Lunar Module back into lunar orbit to join Collins in the Command Module.

7. A felt-tipped pen played a critical role in the historic moon landing.

When Aldrin and Armstrong landed, they accidentally broke off the switch to the circuit breaker, which was needed to activate the engine that would lift them off the moon.

“Since it was electrical, I decided not to put my finger in, or use anything that had metal on the end. I had a felt-tipped pen in the shoulder pocket of my suit that might do the job. After moving the countdown procedure up by a couple of hours in case it didn't work, I inserted the pen into the small opening where the circuit breaker switch should have been, and pushed it in; sure enough, the circuit breaker held. We were going to get off the moon, after all.”

All three astronauts carried the pen. According to EETimes, Collins donated his to the Smithsonian National Air and Space Museum, which he helped found.

But Aldrin held onto his pen, keeping it with the broken breaker switch.

8. Here’s what they left behind 

In addition to leaving the American flag on the moon, Armstrong and Aldrin left their backpacks, a gold olive branch-shaped pin symbolizing peace, messages from 73 world leaders and a patch from the Apollo 1 mission -- which never launched because three U.S. astronauts were killed in a 1967 training exercise.

They also left behind medallions honoring Russian cosmonauts, including Vladimir Komarov and Yuri Gagarin, both of whom died in flight in 1967 and 1968, respectively.

According to NPR, the tragic story goes that Komarov knew he was probably going to die on the 1967 Soyuz 1 mission, but because Gagarin was his backup and he didn't want him to die, Komarov didn't back out of the mission.

9. The computers that were processing Apollo 11 had less power than a cellphone.

The command module computer (or the so-called Apollo Guidance Computer) made it possible for astronauts to enter noun/verb commands to control the spacecraft and navigation.

But, according to Computer Weekly, the "ingenious computer systems" were more basic than what we find in toasters today.

And today’s USBs are more powerful than the computers used to land the first man on the moon, too.

10. In case the worst happened, all three astronauts had a plan to support their families financially.

Without expensive astronaut life insurance, the astronauts got creative about how they were going to support their families if the worst did happen.

The answer: autographs.

According to NPR, during quarantine (about a month before Apollo 11 launched), the famous astronauts signed hundreds of envelopes and gave them to a friend to save.

On big dates, such as the day of the moon landing or the day Apollo 11 launched, their friend would get the autographed envelopes postmarked at the post office and give them to the astronauts’ families.

Luckily, those “life insurance autographs” were not needed.

However, according to space historian Robert Pearlman, those autographs were worth as much as $30,000 in the 1990s.

11. They had to fill out customs and declaration forms when they returned to the U.S.

Just because you make it to the moon and back doesn’t mean you get a pass on the dreaded customs forms.

The astronauts comically noted “Apollo 11” as the flight on their customs form with a departure from “Moon” to Honolulu, Hawaii.

And under “Any other condition on board which may lead to the spread of disease,” the response was: “To be determined.”