Wednesday marks the 47th anniversary of when NASA astronauts first landed on the moon, a giant leap of an accomplishment that still resonates today, over four and a half decades later.

Astronauts Neil Armstrong, Buzz Aldrin, and Michael Collins blasted off from Earth on a massive Saturn V rocket on July 16, 1969. Four days later, the Eagle module landed on the surface with Aldrin and Armstrong inside; Collins stayed behind in the orbiting Columbia craft.

Millions of people back on Earth watched, captivated, as Armstrong was the first down the ladder, then uttered his now-famous line: “That’s one small step for man, one giant leap for mankind.”

Armstrong described the moon’s surface as being “very, very fine-grained as you get close to it— it’s almost like a powder.”

The astronauts eventually returned to Earth, splashing down four days later in the Pacific. On the moon, an American flag and a plaque that read, in part, “We came in peace for all mankind,” remained

Wednesday, 47 years later, Aldrin took to Twitter, posting a short clip of the lunar lander’s descent, followed by Armstrong saying “the Eagle has landed,” as well as a GIF of the ship in orbit around the moon.

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Aldrin, wearing a pair of red, white and blue suspenders, and a black T-shirt with an astronaut and an eagle on it, also appeared in a Facebook Live event commemorating the anniversary Wednesday.

Only 12 people have ever walked on the moon.

NASA also celebrated another important milestone on Wednesday: the 40th anniversary of the Viking 1 lander's arrival on the surface of Mars. Viking 1 and 2 were launched from Earth in 1975, and on July 20, 1976, Viking 1 landed on the red planet-- the first time an American craft had done so. (Its originally scheduled landing date was July 4, 1976.) Viking 1 beamed back pictures, analyzed the planet, and even kept transmitting information until November, 1982.

Follow Rob Verger on Twitter: @robverger