The powerful of Washington, the pioneers of space, and the everyday public crowded into the Washington National Cathedral for a public interfaith memorial for the very private astronaut.
Armstrong, who died last month in Ohio at age 82, walked on the moon in July 1969.
"He's now slipped the bonds of Earth once again, but what a legacy he left," former Treasury Secretary John Snow told the gathering.
Apollo 11 crewmates Buzz Aldrin and Michael Collins and Mercury astronaut John Glenn and about two dozen members of Congress were among the estimated 1,500 people in the cavernous cathedral. A moon rock that the Apollo 11 astronauts gave the church in 1974 is embedded in one of its stained glass windows.
"You have now shown once again the pathway to the stars," Eugene Cernan, the last man to walk on the moon said in a tribute to Armstrong. "As you soar through the heavens beyond even where eagles dare to go, you can now finally put out your hand and touch the face of God."
Cernan was followed by a slow and solemn version of the song "Fly Me to the Moon" by singer Diana Krall. The service also included excerpts from a speech 50 years ago by John F. Kennedy in which he said America chose to send men to the moon not because it was easy, but because it was hard.
NASA administrator Charles Bolden, a former astronaut, said Armstrong's humility and courage "lifted him above the stars." Bolden read a letter from President Barack Obama saying, "the imprint he left on the surface of the moon is matched only by the extraordinary mark he left on ordinary Americans."
Armstrong commanded the historic landing of the Apollo 11 spacecraft on the moon July 20, 1969. His first words after stepping onto the moon are etched in history books: "That's one small step for man, one giant leap for mankind." Armstrong insisted later that he had said "a'' before man, but said he, too, couldn't hear it in the recorded version.
Armstrong and Aldrin spent nearly three hours walking on the lunar surface and left behind a plaque that read: "Here men from the planet Earth first set foot upon the moon. July 1969 A.D. We came in peace for all mankind."
In all, 12 American astronauts walked on the moon before the last moon mission in 1972.