Buzz Aldrin was expected to attend but canceled, the AP reported.
"[It's] wonderful being back. There's a difference this time. I want to turn and ask Neil a question and maybe tell Buzz Aldrin something, and of course, I'm here by myself," Collins said on NASA TV, according to the AP.
Collins was the command module pilot and stayed back on Columbia as Armstrong and Aldrin walked on the moon on July 20, 1969.
Armstrong, who was the mission commander and took the first step on the moon died in 2012.
The event marks the beginning of a week-long celebration of the Apollo 11 historic mission.
It isn't the only commemoration of the historic day.
Model rockets, 5,000 in all, will launch at the same time at the U.S. Space and Rocket Center in Huntsville, Alabama. The Smithsonian's National Air and Space Museum will also unveil Neil Armstrong's newly-restored spacesuit, the AP reported.
You can follow the launch events, moment-by-moment on Twitter as Apollo 50th live tweets.
Credit: DaytonDailyNews
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