[Read all Times reporting on the 50th anniversary of the Apollo 11 moon landing.]

The Apollo 11 moon walk wasn’t the first broadcast sent from space, but in geographic reach, it was the most astonishing. Microwave links, satellites and landlines carried images of Neil Armstrong’s steps around the globe from Australia and the United States to Japan and Europe, even parts of the Eastern Bloc, in virtually real time. This was live TV from more than 200,000 miles away, using the technology of 1969.

Although the experience of watching that event looms large in memory for those who saw it, for NASA historians and other space experts, the preservation of that broadcast has provided its own drama.

On Saturday, the moon landing’s 50th anniversary, three reels of videotape will be auctioned at Sotheby’s, marketed as “the only surviving first-generation recordings of the historic moon walk” and “the earliest, sharpest, and most accurate surviving video images of man’s first steps on the moon.”

According to Sotheby’s, a NASA intern named Gary George bought the recordings as part of a collection of 1,150 reels at a government surplus auction in 1976. He paid $217.77 for all of them. The bidding on Saturday starts at $700,000, and Sotheby’s estimates they will sell for over $1 million.