Monday marks the 40th anniversary of the first landing on the moon, one of mankind’s greatest achievements.

For those old enough to have watched the event, a grainy black and white television broadcast, we lived our lives through Neil Armstrong and Buzz Aldrin that day.

The landing of the lunar module, the first step, the now-famous saying (“One small step for man; one giant leap for mankind...”) and scenes of the two American astronauts bouncing around the barren moon surface are etched in our minds.

The moon landing was the conclusion of a promise made by U.S. president John F. Kennedy in 1961 to first step foot on Earth’s closest celestial body within a decade.

While we glorified in the achievement, there were a few tidbits of information that were overlooked. Like the fact Armstrong had just seconds worth of fuel left when he finally landed the Eagle on the Moon.

So to mark Monday’s 40th anniversary, here are a few other interesting factoids—courtesy of Rocket Men author Craig Nelson.

• The computers used in the Apollo 11 mission had less computing power than today’s cellphone.

• Because Armstrong landed the module so softly, the shock absorbers didn’t compress. That meant his “One small step” was actually a lengthy 3.5 feet from the lander to the surface.

• Planting the American flag, which was made by Sears, was no easy task and it took the efforts of both astronauts to thrust it into the ground. From that scientists learned the Moon’s surface is a thin layer of dust over hard rock.

• When Aldrin joined Armstrong on the surface, he had to make sure not to lock the Eagle’s door because it had no outer handle.

• NASA seated its VIPs three and a half miles from the launchpad when the Apollo mission took off. Scientists and engineers estimated that if the Saturn rockets exploded, they would be able to throw a 100-pound piece of shrapnel three miles. They couldn’t risk the results of an explosion at liftoff.