Armstrong, the first man to walk on the Moon, passed away in hospital in Columbus, Ohio at the age of 82 after suffering complications following surgery earlier this month (Aug12) for blocked coronary arteries.
After hearing the sad news, fellow astronaut Buzz Aldrin, with whom Armstrong made history in 1969 by setting foot on the Moon, released a statement which reads: "Whenever I look at the Moon it reminds me of the moment over four decades ago when I realized that even though we were farther away from earth than two humans had ever been, we were not alone. Virtually the entire world took that memorable journey with us. I know I am joined by millions of others in mourning the passing of a true American hero and the best pilot I ever knew.
"My friend Neil took the small step but giant leap that changed the world and will forever be remembered as a landmark moment in human history. I had truly hoped that in 2019, we would be standing together along with our colleague Mike Collins to commemorate the 50th Anniversary of our moon landing. Regrettably, this is not to be. Neil will most certainly be there with us in spirit."
U.S. President Barack Obama also paid tribute to the spacewalker by stating: "(Wife) Michelle and I were deeply saddened to hear about the passing of Neil Armstrong. Neil was among the greatest of American heroes - not just of his time, but of all time. When he and his fellow crew members lifted off aboard Apollo 11 in 1969, they carried with them the aspirations of an entire nation.
"They set out to show the world that the American spirit can see beyond what seems unimaginable - that with enough drive and ingenuity, anything is possible. And when Neil stepped foot on the surface of the moon for the first time, he delivered a moment of human achievement that will never be forgotten."
Meanwhile, celebrities like Star Trek actor George Takei have also remembered Armstrong's out-of-this-world achievements.
In a Twitter.com post on Saturday (25Aug12), he wrote, "With him, we all took one giant leap towards the heavens. Rest in peace, Neil Armstrong, as you rejoin them", while Transformers star Josh Duhamel added, "One of our greatest heroes died today. RIP Neil Armstrong."
And American Idol host Ryan Seacrest tweeted, "Thanks Neil Armstrong for bringing the moon into our living rooms & curiosity into our minds. One giant loss for mankind."
Armstrong and fellow astronaut Buzz Aldrin made history on 20 July 1969 when they climbed out of Apollo 11's Lunar Module and spent three hours exploring the surface of the Moon, when he famously said, "One small step for man, one giant leap for mankind."
The trip marked the start of a new era for space travel and exploration and Armstrong was later handed numerous U.S. honours, including the Presidential Medal of Freedom and the Congressional Space Medal of Honor. He was also was awarded the Congressional Gold Medal last year (11).