Forty-four isn't exactly a milestone number for celebrations, but Saturday's 44th anniversary of the Apollo 11 lunar landing nevertheless struck a chord — in part because it's the first anniversary that Neil Armstrong, the first man to walk on the moon, wasn't around to celebrate.
"We all miss you, Neil," one of his Apollo 11 crewmates, Buzz Aldrin, wrote Saturday in a Twitter tribute.
Armstrong passed away last August at the age of 82 after suffering heart problems — and in the 11 months since then, there have been multiple memorials held in his honor. But in a way, the Moon Day anniversary is just as much of a memorial to the achievements of Armstrong and Aldrin, as well as Michael Collins, who manned Apollo 11's command module in lunar orbit while the other two walked on the surface below. Moreover, July 20 commemorates the achievements of the thousands of others who worked on Earth to make their "giant leap" possible.
Nearly 200 people who worked on the lunar module at Grumman Aerospace gathered at Florida's Space Coast for a weekend reunion. In Dallas, Love Field's Frontiers of Flight Museum organized a full schedule of talks, workshops and webcasts to mark Moon Day.
Many of Saturday's tributes came in visual form: A classic view of Mission Control's celebration just after Apollo 11's splashdown served as NASA's "Image of the Day." Wired's Adam Mann turned a spotlight on the Hasselblad cameras that recorded the best pictures from the Apollo moon missions. Bad Astronomy blogger Phil Plait features a time-lapse video that was inspired by Collins' adventure in orbit. And Canadian astronaut Chris Hadfield shared a seldom-seen portrait of the Apollo 11 crew that was captured by the late, great Armenian-Canadian photographer Yousuf Karsh.
"44 years ago today Mike, Buzz and Neil took us to the moon. They inspired me like no other. Eternal thanks," Hadfield wrote.
The links below offer more sights, sounds and substance for Moon Day — but the easiest way to celebrate the anniversary is to take the advice of Armstrong's family, particularly on a weekend when the moon is big and bright: "The next time you walk outside on a clear night and see the moon smiling down at you, think of Neil Armstrong and give him a wink."
More about Neil Armstrong and Apollo 11:
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.