WASHINGTON (CNN) -- The first man on the moon marked the 40th anniversary of his historic achievement with characteristic understatement Monday, calling the program that put him on the lunar surface "a good thing to do." 

President Obama welcomes, from left, Buzz Aldrin, Michael Collins and Neil Armstrong. 

Apollo 11 commander Neil Armstrong joined crewmates Michael Collins and Buzz Aldrin at the National Air and Space Museum, capping a day of commemorations that included a stop at the White House. During brief remarks at the museum, he said the mission was the climax of a "staggeringly complex" endeavor that "required the very best in creativity, determination and perseverance that could be assembled in the American workplace." 

"Those successes were very impressive 40 years ago, but they were not miraculous," Armstrong said. "They were the result of the imagination and inventive minds of the people in the Apollo project since its inception eight years earlier." 

The July 20, 1969, moon landing followed four test missions and came just two years after a fire that killed the first Apollo crew. Six lunar landings followed. A seventh flight, Apollo 13, was forced to abort its landing after an oxygen tank explosion crippled the spacecraft; the crew used its lunar lander as a "lifeboat" for much of their harrowing return to Earth. 

Armstrong called the Apollo program "a superb national enterprise" that "left a lasting imprint on society and history." 

"Our knowledge of the moon increased a thousandfold and more," he said. "Technologies were developed for interplanetary navigation and travel. Our home planet has been seen from afar, and that perspective has caused us to think about its and our significance. Children inspired by the excitement of space flight have come to appreciate the wonder of science, the beauty of mathematics and the precision of engineering." 
Where?
a stop at the White House